More refactoring

Signed-off-by: Mattias Andrée <maandree@kth.se>

8 files changed, 1707 insertions, 0 deletions

diff --git a/src/servers/coopgamma.c b/src/servers/coopgamma.c
new file mode 100644
index 0000000..7f8b815
--- /dev/null
+++ b/src/servers/coopgamma.c
@@ -0,0 +1,601 @@
+/**
+ * coopgammad -- Cooperative gamma server
+ * Copyright (C) 2016  Mattias Andrée (maandree@kth.se)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include "coopgamma.h"
+#include "gamma.h"
+#include "../state.h"
+#include "../communication.h"
+#include "../util.h"
+#include "../types/output.h"
+
+#include <libclut.h>
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+
+
+/**
+ * Apply a filter on top of another filter
+ * 
+ * @param  dest         The output for the resulting ramp-trio, must be initialised
+ * @param  application  The red, green and blue ramps, as one single raw array,
+ *                      of the filter that should be applied
+ * @param  depth        -1: `float` stops
+ *                      -2: `double` stops
+ *                      Other: the number of bits of each (integral) stop
+ * @param  base         The CLUT on top of which the new filter should be applied,
+ *                      this can be the same pointer as `dest`
+ */
+static void apply_filter(union gamma_ramps* restrict dest, void* restrict application,
+			 int depth, union gamma_ramps* restrict base)
+{
+  union gamma_ramps app;
+  size_t bytedepth;
+  size_t red_width, green_width, blue_width;
+  
+  if (depth == -1)
+    bytedepth = sizeof(float);
+  else if (depth == -2)
+    bytedepth = sizeof(double);
+  else
+    bytedepth = (size_t)depth / 8;
+  
+  red_width   = (app.u8.red_size   = base->u8.red_size)   * bytedepth;
+  green_width = (app.u8.green_size = base->u8.green_size) * bytedepth;
+  blue_width  = (app.u8.blue_size  = base->u8.blue_size)  * bytedepth;
+  
+  app.u8.red   = application;
+  app.u8.green = app.u8.red   + red_width;
+  app.u8.blue  = app.u8.green + green_width;
+  
+  if (dest != base)
+    {
+      memcpy(dest->u8.red,   base->u8.red,   red_width);
+      memcpy(dest->u8.green, base->u8.green, green_width);
+      memcpy(dest->u8.blue,  base->u8.blue,  blue_width);
+    }
+  
+  switch (depth)
+    {
+    case 8:
+      libclut_apply(&(dest->u8), UINT8_MAX, uint8_t, &(app.u8), UINT8_MAX, uint8_t, 1, 1, 1);
+      break;
+    case 16:
+      libclut_apply(&(dest->u16), UINT16_MAX, uint16_t, &(app.u16), UINT16_MAX, uint16_t, 1, 1, 1);
+      break;
+    case 32:
+      libclut_apply(&(dest->u32), UINT32_MAX, uint32_t, &(app.u32), UINT32_MAX, uint32_t, 1, 1, 1);
+      break;
+    case 64:
+      libclut_apply(&(dest->u64), UINT64_MAX, uint64_t, &(app.u64), UINT64_MAX, uint64_t, 1, 1, 1);
+      break;
+    case -1:
+      libclut_apply(&(dest->f), 1.0f, float, &(app.d), 1.0f, float, 1, 1, 1);
+      break;
+    case -2:
+      libclut_apply(&(dest->d), (double)1, double, &(app.f), (double)1, double, 1, 1, 1);
+      break;
+    default:
+      abort();
+    }
+}
+
+
+
+/**
+ * Remove a filter from an output
+ * 
+ * @param   out     The output
+ * @param   filter  The filter
+ * @return          The index of the filter, `out->table_size` if not found
+ */
+static ssize_t remove_filter(struct output* restrict out, struct filter* restrict filter)
+{
+  size_t i, n = out->table_size;
+  
+  for (i = 0; i < n; i++)
+    if (!strcmp(filter->class, out->table_filters[i].class))
+      break;
+  
+  if (i == out->table_size)
+    {
+      fprintf(stderr, "%s: ignoring attempt to removing non-existing filter on CRTC %s: %s",
+	      argv0, out->name, filter->class);
+      return (ssize_t)(out->table_size);
+    }
+  
+  filter_destroy(out->table_filters + i);
+  libgamma_gamma_ramps8_destroy(&(out->table_sums[i].u8));
+  
+  n = n - i - 1;
+  memmove(out->table_filters + i, out->table_filters + i + 1, n * sizeof(*(out->table_filters)));
+  memmove(out->table_sums    + i, out->table_sums    + i + 1, n * sizeof(*(out->table_sums)));
+  out->table_size--;
+  
+  return (ssize_t)i;
+}
+
+
+/**
+ * Add a filter to an output
+ * 
+ * @param   out     The output
+ * @param   filter  The filter
+ * @return          The index given to the filter, -1 on error
+ */
+static ssize_t add_filter(struct output* restrict out, struct filter* restrict filter)
+{
+  size_t i, n = out->table_size;
+  int r = -1;
+  
+  /* Remove? */
+  if (filter->lifespan == LIFESPAN_REMOVE)
+    return remove_filter(out, filter);
+  
+  /* Update? */
+  for (i = 0; i < n; i++)
+    if (!strcmp(filter->class, out->table_filters[i].class))
+      break;
+  if (i != n)
+    {
+      filter_destroy(out->table_filters + i);
+      out->table_filters[i] = *filter;
+      return (ssize_t)i;
+    }
+  
+  /* Add! */
+  for (i = 0; i < n; i++)
+    if (filter->priority > out->table_filters[i].priority)
+      break;
+  
+  if (n == out->table_alloc)
+    {
+      void* new;
+      
+      new = realloc(out->table_filters, (n + 10) * sizeof(*(out->table_filters)));
+      if (new == NULL)
+	return -1;
+      out->table_filters = new;
+      
+      new = realloc(out->table_sums, (n + 10) * sizeof(*(out->table_sums)));
+      if (new == NULL)
+	return -1;
+      out->table_sums = new;
+      
+      out->table_alloc += 10;
+    }
+  
+  memmove(out->table_filters + i + 1, out->table_filters + i, (n - i) * sizeof(*(out->table_filters)));
+  memmove(out->table_sums    + i + 1, out->table_sums    + i, (n - i) * sizeof(*(out->table_sums)));
+  out->table_size++;
+  
+  COPY_RAMP_SIZES(&(out->table_sums[i].u8), out);
+  switch (out->depth)
+    {
+    case  8:  r = libgamma_gamma_ramps8_initialise(&(out->table_sums[i].u8));    break;
+    case 16:  r = libgamma_gamma_ramps16_initialise(&(out->table_sums[i].u16));  break;
+    case 32:  r = libgamma_gamma_ramps32_initialise(&(out->table_sums[i].u32));  break;
+    case 64:  r = libgamma_gamma_ramps64_initialise(&(out->table_sums[i].u64));  break;
+    case -1:  r = libgamma_gamma_rampsf_initialise(&(out->table_sums[i].f));     break;
+    case -2:  r = libgamma_gamma_rampsd_initialise(&(out->table_sums[i].d));     break;
+    default:
+      abort();
+    }
+  if (r < 0)
+    return -1;
+  
+  out->table_filters[i] = *filter;
+  
+  return (ssize_t)i;
+}
+
+
+/**
+ * Make identity mapping ramps
+ * 
+ * @param   ramps   Output parameter for the ramps
+ * @param   output  The output for which the ramps shall be configured
+ * @return          Zero on success, -1 on error
+ */
+static int make_plain_ramps(union gamma_ramps* restrict ramps, struct output* restrict output)
+{
+  COPY_RAMP_SIZES(&(ramps->u8), output);
+  switch (output->depth)
+    {
+    case 8:
+      if (libgamma_gamma_ramps8_initialise(&(ramps->u8)))
+	return -1;
+      libclut_start_over(&(ramps->u8), UINT8_MAX, uint8_t, 1, 1, 1);
+      break;
+    case 16:
+      if (libgamma_gamma_ramps16_initialise(&(ramps->u16)))
+	return -1;
+      libclut_start_over(&(ramps->u16), UINT16_MAX, uint16_t, 1, 1, 1);
+      break;
+    case 32:
+      if (libgamma_gamma_ramps32_initialise(&(ramps->u32)))
+	return -1;
+      libclut_start_over(&(ramps->u32), UINT32_MAX, uint32_t, 1, 1, 1);
+      break;
+    case 64:
+      if (libgamma_gamma_ramps64_initialise(&(ramps->u64)))
+	return -1;
+      libclut_start_over(&(ramps->u64), UINT64_MAX, uint64_t, 1, 1, 1);
+      break;
+    case -1:
+      if (libgamma_gamma_rampsf_initialise(&(ramps->f)))
+	return -1;
+      libclut_start_over(&(ramps->f), 1.0f, float, 1, 1, 1);
+      break;
+    case -2:
+      if (libgamma_gamma_rampsd_initialise(&(ramps->d)))
+	return -1;
+      libclut_start_over(&(ramps->d), (double)1, double, 1, 1, 1);
+      break;
+    default:
+      abort();
+    }
+  return 0;
+}
+
+
+
+/**
+ * Handle a closed connection
+ * 
+ * @param   client  The file descriptor for the client
+ * @return          Zero on success, -1 on error
+ */
+int connection_closed(int client)
+{
+  size_t i, j, k;
+  int remove;
+  
+  for (i = 0; i < outputs_n; i++)
+    {
+      struct output* output = outputs + i;
+      ssize_t updated = -1;
+      for (j = k = 0; j < output->table_size; j += !remove, k++)
+	{
+	  remove = output->table_filters[j].client == client;
+	  remove = remove && (output->table_filters[j].lifespan == LIFESPAN_UNTIL_DEATH);
+	  if (remove)
+	    {
+	      filter_destroy(output->table_filters + j);
+	      libgamma_gamma_ramps8_destroy(&(output->table_sums[j].u8));
+	      output->table_size -= 1;
+	      if (updated == -1)
+		updated = (ssize_t)j;
+	    }
+	  output->table_filters[j] = output->table_filters[k];
+	  output->table_sums[j]    = output->table_sums[k];
+	}
+      if (updated >= 0)
+	if (flush_filters(output, (size_t)updated) < 0)
+	  return -1;
+    }
+  
+  return 0;
+}
+
+
+/**
+ * Handle a ‘Command: get-gamma’ message
+ * 
+ * @param   conn           The index of the connection
+ * @param   message_id     The value of the ‘Message ID’ header
+ * @param   crtc           The value of the ‘CRTC’ header
+ * @param   coalesce       The value of the ‘Coalesce’ header
+ * @param   high_priority  The value of the ‘High priority’ header
+ * @param   low_priority   The value of the ‘Low priority’ header
+ * @return                 Zero on success (even if ignored), -1 on error,
+ *                         1 if connection closed
+ */
+int handle_get_gamma(size_t conn, const char* restrict message_id, const char* restrict crtc,
+		     const char* restrict coalesce, const char* restrict high_priority,
+		     const char* restrict low_priority)
+{
+  struct output* restrict output;
+  int64_t high, low;
+  int coal;
+  char* restrict buf;
+  size_t start, end, len, n, i;
+  char depth[3];
+  char tables[sizeof("Tables: \n") + 3 * sizeof(size_t)];
+  
+  if (crtc          == NULL)  return send_error("protocol error: 'CRTC' header omitted");
+  if (coalesce      == NULL)  return send_error("protocol error: 'Coalesce' header omitted");
+  if (high_priority == NULL)  return send_error("protocol error: 'High priority' header omitted");
+  if (low_priority  == NULL)  return send_error("protocol error: 'Low priority' header omitted");
+  
+  high = (int64_t)atoll(high_priority);
+  low  = (int64_t)atoll(low_priority);
+  
+  if (!strcmp(coalesce, "yes"))
+    coal = 1;
+  else if (!strcmp(coalesce, "no"))
+    coal = 0;
+  else
+    return send_error("protocol error: recognised value for 'Coalesce' header");
+  
+  output = output_find_by_name(crtc, outputs, outputs_n);
+  if (output == NULL)
+    return send_error("selected CRTC does not exist");
+  else if (output->supported == LIBGAMMA_NO)
+    return send_error("selected CRTC does not support gamma adjustments");
+  
+  for (start = 0; start < output->table_size; start++)
+    if (output->table_filters[start].priority <= high)
+      break;
+  
+  for (end = output->table_size; end > 0; end--)
+    if (output->table_filters[end - 1].priority >= low)
+      break;
+  
+  switch (output->depth)
+    {
+    case -2:  strcpy(depth, "d");  break;
+    case -1:  strcpy(depth, "f");  break;
+    default:
+      sprintf(depth, "%i", output->depth);
+      break;
+    }
+  
+  if (coal)
+    {
+      *tables = '\0';
+      n = output->ramps_size;
+    }
+  else
+    {
+      sprintf(tables, "Tables: %zu\n", end - start);
+      n = (sizeof(int64_t) + output->ramps_size) * (end - start);
+      for (i = start; i < end; i++)
+	n += strlen(output->table_filters[i].class) + 1;
+    }
+  
+  MAKE_MESSAGE(&buf, &n, 0,
+	       "In response to: %s\n"
+	       "Depth: %s\n"
+	       "Red size: %zu\n"
+	       "Green size: %zu\n"
+	       "Blue size: %zu\n"
+	       "%s"
+	       "Length: %zu\n"
+	       "\n",
+	       message_id, depth, output->red_size, output->green_size,
+	       output->blue_size, tables, n);
+  
+  if (coal)
+    {
+      if (start == 0)
+	memcpy(buf + n, output->table_sums[end].u8.red, output->ramps_size);
+      else
+	{
+	  union gamma_ramps ramps;
+	  if (make_plain_ramps(&ramps, output))
+	    {
+	      int saved_errno = errno;
+	      free(buf);
+	      errno = saved_errno;
+	      return -1;
+	    }
+	  for (i = start; i < end; i++)
+	    apply_filter(&ramps, output->table_filters[i].ramps, output->depth, &ramps);
+	  memcpy(buf + n, ramps.u8.red, output->ramps_size);
+	  libgamma_gamma_ramps8_destroy(&(ramps.u8));
+	}
+      n += output->ramps_size;
+    }
+  else
+    for (i = start; i < end; i++)
+      {
+#if defined(__clang__)
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wcast-align"
+#endif
+	*(int64_t*)(buf + n) = output->table_filters[i].priority;
+#if defined(__clang__)
+# pragma GCC diagnostic pop
+#endif
+	n += sizeof(int64_t);
+	len = strlen(output->table_filters[i].class) + 1;
+	memcpy(buf + n, output->table_filters[i].class, len);
+	n += len;
+	memcpy(buf + n, output->table_filters[i].ramps, output->ramps_size);
+	n += output->ramps_size;
+      }
+  
+  return send_message(conn, buf, n);
+}
+
+
+/**
+ * Handle a ‘Command: set-gamma’ message
+ * 
+ * @param   conn        The index of the connection
+ * @param   message_id  The value of the ‘Message ID’ header
+ * @param   crtc        The value of the ‘CRTC’ header
+ * @param   priority    The value of the ‘Priority’ header
+ * @param   class       The value of the ‘Class’ header
+ * @param   lifespan    The value of the ‘Lifespan’ header
+ * @return              Zero on success (even if ignored), -1 on error,
+ *                      1 if connection closed
+ */
+int handle_set_gamma(size_t conn, const char* restrict message_id, const char* restrict crtc,
+		     const char* restrict priority, const char* restrict class, const char* restrict lifespan)
+{
+  struct message* restrict msg = inbound + conn;
+  struct output* restrict output = NULL;
+  struct filter filter;
+  char* restrict p;
+  char* restrict q;
+  int saved_errno;
+  ssize_t r;
+  
+  if (crtc     == NULL)  return send_error("protocol error: 'CRTC' header omitted");
+  if (class    == NULL)  return send_error("protocol error: 'Class' header omitted");
+  if (lifespan == NULL)  return send_error("protocol error: 'Lifespan' header omitted");
+  
+  filter.client   = connections[conn];
+  filter.priority = priority == NULL ? 0 : (int64_t)atoll(priority);
+  filter.ramps    = NULL;
+  
+  output = output_find_by_name(crtc, outputs, outputs_n);
+  if (output == NULL)
+    return send_error("CRTC does not exists");
+  
+  p = strstr(class, "::");
+  if ((p == NULL) || (p == class))
+    return send_error("protocol error: malformatted value for 'Class' header");
+  q = strstr(p + 2, "::");
+  if ((q == NULL) || (q == p))
+    return send_error("protocol error: malformatted value for 'Class' header");
+  
+  if (!strcmp(lifespan, "until-removal"))
+    filter.lifespan = LIFESPAN_UNTIL_REMOVAL;
+  else if (!strcmp(lifespan, "until-death"))
+    filter.lifespan = LIFESPAN_UNTIL_DEATH;
+  else if (!strcmp(lifespan, "remove"))
+    filter.lifespan = LIFESPAN_REMOVE;
+  else
+    return send_error("protocol error: recognised value for 'Lifespan' header");
+  
+  if (filter.lifespan == LIFESPAN_REMOVE)
+    {
+      if (msg->payload_size)
+	fprintf(stderr, "%s: ignoring superfluous payload on Command: set-gamma message with "
+			"Lifespan: remove\n", argv0);
+      if (priority != NULL)
+	fprintf(stderr, "%s: ignoring superfluous Priority header on Command: set-gamma message with "
+			"Lifespan: remove\n", argv0);
+    }
+  else if (msg->payload_size != output->ramps_size)
+    return send_error("invalid payload: size of message payload does matched the expectancy");
+  else if (priority == NULL)
+    return send_error("protocol error: 'Priority' header omitted");
+  
+  filter.class = memdup(class, strlen(class) + 1);
+  if (filter.class == NULL)
+    goto fail;
+  
+  if (filter.lifespan != LIFESPAN_REMOVE)
+    {
+      filter.ramps = memdup(msg->payload, msg->payload_size);
+      if (filter.ramps == NULL)
+	goto fail;
+    }
+  
+  if ((r = add_filter(output, &filter)) < 0)
+    goto fail;
+  filter.class = NULL;
+  filter.ramps = NULL;
+  if (flush_filters(output, (size_t)r))
+    goto fail;
+  
+  return send_errno(0);
+  
+ fail:
+  saved_errno = errno;
+  send_errno(saved_errno);
+  free(filter.class);
+  free(filter.ramps);
+  errno = saved_errno;
+  return -1;
+}
+
+
+
+/**
+ * Recalculate the resulting gamma and
+ * update push the new gamma ramps to the CRTC
+ * 
+ * @param   output         The output
+ * @param   first_updated  The index of the first added or removed filter
+ * @return                 Zero on success, -1 on error
+ */
+int flush_filters(struct output* restrict output, size_t first_updated)
+{
+  union gamma_ramps plain;
+  union gamma_ramps* last;
+  size_t i;
+  
+  if (first_updated == 0)
+    {
+      if (make_plain_ramps(&plain, output) < 0)
+	return -1;
+      last = &plain;
+    }
+  else
+    last = output->table_sums + (first_updated - 1);
+  
+  for (i = first_updated; i < output->table_size; i++)
+    {
+      apply_filter(output->table_sums + i, output->table_filters[i].ramps, output->depth, last);
+      last = output->table_sums + i;
+    }
+  
+  set_gamma(output, last);
+  
+  if (first_updated == 0)
+    libgamma_gamma_ramps8_destroy(&(plain.u8));
+  
+  return 0;
+}
+
+
+
+/**
+ * Preserve current gamma ramps at priority 0 for all outputs
+ * 
+ * @return  Zero on success, -1 on error
+ */
+int preserve_gamma(void)
+{
+  size_t i;
+  
+  for (i = 0; i < outputs_n; i++)
+    {
+      struct filter filter = {
+	.client   = -1,
+	.priority = 0,
+	.class    = NULL,
+	.lifespan = LIFESPAN_UNTIL_REMOVAL,
+	.ramps    = NULL
+      };
+      outputs[i].table_filters = calloc(4, sizeof(*(outputs[i].table_filters)));
+      outputs[i].table_sums = calloc(4, sizeof(*(outputs[i].table_sums)));
+      outputs[i].table_alloc = 4;
+      outputs[i].table_size = 1;
+      filter.class = memdup(PKGNAME "::" COMMAND "::preserved", sizeof(PKGNAME "::" COMMAND "::preserved"));
+      if (filter.class == NULL)
+	return -1;
+      filter.ramps = memdup(outputs[i].saved_ramps.u8.red, outputs[i].ramps_size);
+      if (filter.ramps == NULL)
+	return -1;
+      outputs[i].table_filters[0] = filter;
+      COPY_RAMP_SIZES(&(outputs[i].table_sums[0].u8), outputs + i);
+      if (!gamma_ramps_unmarshal(outputs[i].table_sums, outputs[i].saved_ramps.u8.red, outputs[i].ramps_size))
+	return -1;
+    }
+  
+  return 0;
+}
+
diff --git a/src/servers/coopgamma.h b/src/servers/coopgamma.h
new file mode 100644
index 0000000..5a9f7d9
--- /dev/null
+++ b/src/servers/coopgamma.h
@@ -0,0 +1,101 @@
+/**
+ * coopgammad -- Cooperative gamma server
+ * Copyright (C) 2016  Mattias Andrée (maandree@kth.se)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef SERVERS_COOPGAMMA_H
+#define SERVERS_COOPGAMMA_H
+
+
+#include "../types/output.h"
+
+#include <stddef.h>
+
+
+
+#ifndef GCC_ONLY
+# if defined(__GNUC__) && !defined(__clang__)
+#  define GCC_ONLY(...)  __VA_ARGS__
+# else
+#  define GCC_ONLY(...)  /* nothing */
+# endif
+#endif
+
+
+
+/**
+ * Handle a closed connection
+ * 
+ * @param   client  The file descriptor for the client
+ * @return          Zero on success, -1 on error
+ */
+int connection_closed(int client);
+
+/**
+ * Handle a ‘Command: get-gamma’ message
+ * 
+ * @param   conn           The index of the connection
+ * @param   message_id     The value of the ‘Message ID’ header
+ * @param   crtc           The value of the ‘CRTC’ header
+ * @param   coalesce       The value of the ‘Coalesce’ header
+ * @param   high_priority  The value of the ‘High priority’ header
+ * @param   low_priority   The value of the ‘Low priority’ header
+ * @return                 Zero on success (even if ignored), -1 on error,
+ *                         1 if connection closed
+ */
+GCC_ONLY(__attribute__((nonnull(2))))
+int handle_get_gamma(size_t conn, const char* restrict message_id, const char* restrict crtc,
+		     const char* restrict coalesce, const char* restrict high_priority,
+		     const char* restrict low_priority);
+
+/**
+ * Handle a ‘Command: set-gamma’ message
+ * 
+ * @param   conn        The index of the connection
+ * @param   message_id  The value of the ‘Message ID’ header
+ * @param   crtc        The value of the ‘CRTC’ header
+ * @param   priority    The value of the ‘Priority’ header
+ * @param   class       The value of the ‘Class’ header
+ * @param   lifespan    The value of the ‘Lifespan’ header
+ * @return              Zero on success (even if ignored), -1 on error,
+ *                      1 if connection closed
+ */
+GCC_ONLY(__attribute__((nonnull(2))))
+int handle_set_gamma(size_t conn, const char* restrict message_id, const char* restrict crtc,
+		     const char* restrict priority, const char* restrict class, const char* restrict lifespan);
+
+
+/**
+ * Recalculate the resulting gamma and
+ * update push the new gamma ramps to the CRTC
+ * 
+ * @param   output         The output
+ * @param   first_updated  The index of the first added or removed filter
+ * @return                 Zero on success, -1 on error
+ */
+GCC_ONLY(__attribute__((nonnull)))
+int flush_filters(struct output* restrict output, size_t first_updated);
+
+
+/**
+ * Preserve current gamma ramps at priority 0 for all outputs
+ * 
+ * @return  Zero on success, -1 on error
+ */
+int preserve_gamma(void);
+
+
+#endif
+
diff --git a/src/servers/crtc.c b/src/servers/crtc.c
new file mode 100644
index 0000000..2e884a8
--- /dev/null
+++ b/src/servers/crtc.c
@@ -0,0 +1,129 @@
+/**
+ * coopgammad -- Cooperative gamma server
+ * Copyright (C) 2016  Mattias Andrée (maandree@kth.se)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include "crtc.h"
+#include "../state.h"
+#include "../communication.h"
+
+#include <errno.h>
+#include <string.h>
+
+
+
+/**
+ * Handle a ‘Command: enumerate-crtcs’ message
+ * 
+ * @param   conn        The index of the connection
+ * @param   message_id  The value of the ‘Message ID’ header
+ * @return              Zero on success (even if ignored), -1 on error,
+ *                      1 if connection closed
+ */
+int handle_enumerate_crtcs(size_t conn, const char* restrict message_id)
+{
+  size_t i, n = 0, len;
+  char* restrict buf;
+  
+  for (i = 0; i < outputs_n; i++)
+    n += strlen(outputs[i].name) + 1;
+  
+  MAKE_MESSAGE(&buf, &n, 0,
+	       "Command: crtc-enumeration\n"
+	       "In response to: %s\n"
+	       "Length: %zu\n"
+	       "\n",
+	       message_id, n);
+  
+  for (i = 0; i < outputs_n; i++)
+    {
+      len = strlen(outputs[i].name);
+      memcpy(buf + n, outputs[i].name, len);
+      buf[n + len] = '\n';
+      n += len + 1;
+    }
+  
+  return send_message(conn, buf, n);
+}
+
+
+/**
+ * Get the name of a CRTC
+ * 
+ * @param   info  Information about the CRTC
+ * @param   crtc  libgamma's state for the CRTC
+ * @return        The name of the CRTC, `NULL` on error
+ */
+char* get_crtc_name(const libgamma_crtc_information_t* restrict info,
+		    const libgamma_crtc_state_t* restrict crtc)
+{
+  if ((info->edid_error == 0) && (info->edid != NULL))
+    return libgamma_behex_edid(info->edid, info->edid_length);
+  else if ((info->connector_name_error == 0) && (info->connector_name != NULL))
+    {
+      char* name = malloc(3 * sizeof(size_t) + strlen(info->connector_name) + 2);
+      if (name != NULL)
+	sprintf(name, "%zu.%s", crtc->partition->partition, info->connector_name);
+      return name;
+    }
+  else
+    {
+      char* name = malloc(2 * 3 * sizeof(size_t) + 2);
+      if (name != NULL)
+	sprintf(name, "%zu.%zu", crtc->partition->partition, crtc->crtc);
+      return name;
+    }
+}
+
+
+/**
+ * Get partitions and CRTC:s
+ * 
+ * @return   Zero on success, -1 on error
+ */
+int initialise_crtcs(void)
+{
+  size_t i, j, n, n0;
+  int gerror;
+  
+  /* Get partitions */
+  if (site.partitions_available)
+    if (!(partitions = calloc(site.partitions_available, sizeof(*partitions))))
+      goto fail;
+  for (i = 0; i < site.partitions_available; i++)
+    {
+      if ((gerror = libgamma_partition_initialise(partitions + i, &site, i)))
+	goto fail_libgamma;
+      outputs_n += partitions[i].crtcs_available;
+    }
+  
+  /* Get CRTC:s */
+  if (outputs_n)
+    if (!(crtcs = calloc(outputs_n, sizeof(*crtcs))))
+      goto fail;
+  for (i = 0, j = n = 0; i < site.partitions_available; i++)
+    for (n0 = n, n += partitions[i].crtcs_available; j < n; j++)
+      if ((gerror = libgamma_crtc_initialise(crtcs + j, partitions + i, j - n0)))
+	goto fail_libgamma;
+  
+  return 0;
+  
+ fail_libgamma:
+  libgamma_perror(argv0, gerror);
+  errno = 0;
+ fail:
+  return -1;
+}
+
diff --git a/src/servers/crtc.h b/src/servers/crtc.h
new file mode 100644
index 0000000..4c96045
--- /dev/null
+++ b/src/servers/crtc.h
@@ -0,0 +1,67 @@
+/**
+ * coopgammad -- Cooperative gamma server
+ * Copyright (C) 2016  Mattias Andrée (maandree@kth.se)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef SERVERS_CRTC_H
+#define SERVERS_CRTC_H
+
+
+#include <libgamma.h>
+
+
+
+#ifndef GCC_ONLY
+# if defined(__GNUC__) && !defined(__clang__)
+#  define GCC_ONLY(...)  __VA_ARGS__
+# else
+#  define GCC_ONLY(...)  /* nothing */
+# endif
+#endif
+
+
+
+/**
+ * Handle a ‘Command: enumerate-crtcs’ message
+ * 
+ * @param   conn        The index of the connection
+ * @param   message_id  The value of the ‘Message ID’ header
+ * @return              Zero on success (even if ignored), -1 on error,
+ *                      1 if connection closed
+ */
+GCC_ONLY(__attribute__((nonnull)))
+int handle_enumerate_crtcs(size_t conn, const char* restrict message_id);
+
+/**
+ * Get the name of a CRTC
+ * 
+ * @param   info  Information about the CRTC
+ * @param   crtc  libgamma's state for the CRTC
+ * @return        The name of the CRTC, `NULL` on error
+ */
+GCC_ONLY(__attribute__((nonnull)))
+char* get_crtc_name(const libgamma_crtc_information_t* restrict info,
+		    const libgamma_crtc_state_t* restrict crtc);
+
+/**
+ * Get partitions and CRTC:s
+ * 
+ * @return   Zero on success, -1 on error
+ */
+int initialise_crtcs(void);
+
+
+#endif
+
diff --git a/src/servers/gamma.c b/src/servers/gamma.c
new file mode 100644
index 0000000..95130e6
--- /dev/null
+++ b/src/servers/gamma.c
@@ -0,0 +1,279 @@
+/**
+ * coopgammad -- Cooperative gamma server
+ * Copyright (C) 2016  Mattias Andrée (maandree@kth.se)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include "gamma.h"
+#include "crtc.h"
+#include "../state.h"
+#include "../communication.h"
+
+#include <errno.h>
+#include <string.h>
+
+
+
+#if defined(__clang__)
+# pragma GCC diagnostic ignored "-Wswitch-enum"
+#endif
+
+
+
+/**
+ * Handle a ‘Command: set-gamma’ message
+ * 
+ * @param   conn        The index of the connection
+ * @param   message_id  The value of the ‘Message ID’ header
+ * @param   crtc        The value of the ‘CRTC’ header
+ * @return              Zero on success (even if ignored), -1 on error,
+ *                      1 if connection closed
+ */
+int handle_get_gamma_info(size_t conn, const char* restrict message_id, const char* restrict crtc)
+{
+  struct output* restrict output;
+  char* restrict buf;
+  char depth[3];
+  const char* supported;
+  size_t n;
+  
+  if (crtc == NULL)  return send_error("protocol error: 'CRTC' header omitted");
+  
+  output = output_find_by_name(crtc, outputs, outputs_n);
+  if (output == NULL)
+    return send_error("selected CRTC does not exist");
+  
+  switch (output->depth)
+    {
+    case -2:  strcpy(depth, "d");  break;
+    case -1:  strcpy(depth, "f");  break;
+    default:
+      sprintf(depth, "%i", output->depth);
+      break;
+    }
+  
+  switch (output->supported)
+    {
+    case LIBGAMMA_YES:    supported = "yes";    break;
+    case LIBGAMMA_NO:     supported = "no";     break;
+    default:              supported = "maybe";  break;
+    }
+  
+  MAKE_MESSAGE(&buf, &n, 0,
+	       "In response to: %s\n"
+	       "Cooperative: yes\n" /* In mds: say ‘no’, mds-coopgamma changes to ‘yes’.” */
+	       "Depth: %s\n"
+	       "Red size: %zu\n"
+	       "Green size: %zu\n"
+	       "Blue size: %zu\n"
+	       "Gamma support: %s\n"
+	       "\n",
+	       message_id, depth, output->red_size, output->green_size,
+	       output->blue_size, supported);
+  
+  return send_message(conn, buf, n);
+}
+
+
+/**
+ * Set the gamma ramps on an output
+ * 
+ * @param  output  The output
+ * @param  ramps   The gamma ramps
+ */
+void set_gamma(const struct output* restrict output, const union gamma_ramps* restrict ramps)
+{
+  int r = 0;
+  
+  if (!connected)
+    return;
+  
+  switch (output->depth)
+    {
+    case  8:  r = libgamma_crtc_set_gamma_ramps8(output->crtc,  ramps->u8);   break;
+    case 16:  r = libgamma_crtc_set_gamma_ramps16(output->crtc, ramps->u16);  break;
+    case 32:  r = libgamma_crtc_set_gamma_ramps32(output->crtc, ramps->u32);  break;
+    case 64:  r = libgamma_crtc_set_gamma_ramps64(output->crtc, ramps->u64);  break;
+    case -1:  r = libgamma_crtc_set_gamma_rampsf(output->crtc,  ramps->f);    break;
+    case -2:  r = libgamma_crtc_set_gamma_rampsd(output->crtc,  ramps->d);    break;
+    default:
+      abort();
+    }
+  if (r)
+    libgamma_perror(argv0, r); /* Not fatal */
+}
+
+
+
+/**
+ * Store all current gamma ramps
+ * 
+ * @return  Zero on success, -1 on error
+ */
+int initialise_gamma_info(void)
+{
+  libgamma_crtc_information_t info;
+  int saved_errno;
+  size_t i;
+  
+  for (i = 0; i < outputs_n; i++)
+    {
+      libgamma_get_crtc_information(&info, crtcs + i,
+				    LIBGAMMA_CRTC_INFO_EDID |
+				    LIBGAMMA_CRTC_INFO_MACRO_RAMP |
+				    LIBGAMMA_CRTC_INFO_GAMMA_SUPPORT |
+				    LIBGAMMA_CRTC_INFO_CONNECTOR_NAME);
+      outputs[i].depth       = info.gamma_depth_error   ? 0 : info.gamma_depth;
+      outputs[i].red_size    = info.gamma_size_error    ? 0 : info.red_gamma_size;
+      outputs[i].green_size  = info.gamma_size_error    ? 0 : info.green_gamma_size;
+      outputs[i].blue_size   = info.gamma_size_error    ? 0 : info.blue_gamma_size;
+      outputs[i].supported   = info.gamma_support_error ? 0 : info.gamma_support;
+      if (outputs[i].depth      == 0 || outputs[i].red_size  == 0 ||
+	  outputs[i].green_size == 0 || outputs[i].blue_size == 0)
+	outputs[i].supported = 0;
+      outputs[i].name        = get_crtc_name(&info, crtcs + i);
+      saved_errno = errno;
+      outputs[i].crtc        = crtcs + i;
+      libgamma_crtc_information_destroy(&info);
+      outputs[i].ramps_size = outputs[i].red_size + outputs[i].green_size + outputs[i].blue_size;
+      switch (outputs[i].depth)
+	{
+	default:
+	  outputs[i].depth = 64;
+	  /* Fall through */
+	case  8:
+	case 16:
+	case 32:
+	case 64:  outputs[i].ramps_size *= (size_t)(outputs[i].depth / 8);  break;
+	case -2:  outputs[i].ramps_size *= sizeof(double);                  break;
+	case -1:  outputs[i].ramps_size *= sizeof(float);                   break;
+	}
+      errno = saved_errno;
+      if (outputs[i].name == NULL)
+	return -1;
+    }
+  
+  return 0;
+}
+
+
+/**
+ * Store all current gamma ramps
+ */
+void store_gamma(void)
+{
+  int gerror;
+  size_t i;
+  
+#define LOAD_RAMPS(SUFFIX, MEMBER) \
+  do \
+    { \
+      libgamma_gamma_ramps##SUFFIX##_initialise(&(outputs[i].saved_ramps.MEMBER)); \
+      gerror = libgamma_crtc_get_gamma_ramps##SUFFIX(outputs[i].crtc, &(outputs[i].saved_ramps.MEMBER)); \
+      if (gerror) \
+	{ \
+	  libgamma_perror(argv0, gerror); \
+	  outputs[i].supported = LIBGAMMA_NO; \
+	  libgamma_gamma_ramps##SUFFIX##_destroy(&(outputs[i].saved_ramps.MEMBER)); \
+	  memset(&(outputs[i].saved_ramps.MEMBER), 0, sizeof(outputs[i].saved_ramps.MEMBER)); \
+	} \
+    } \
+  while (0)
+  
+  for (i = 0; i < outputs_n; i++)
+    {
+      if (outputs[i].supported == LIBGAMMA_NO)
+	continue;
+      
+      switch (outputs[i].depth)
+	{
+	case 64:  LOAD_RAMPS(64, u64);  break;
+	case 32:  LOAD_RAMPS(32, u32);  break;
+	case 16:  LOAD_RAMPS(16, u16);  break;
+	case  8:  LOAD_RAMPS( 8, u8);   break;
+	case -2:  LOAD_RAMPS(d, d);     break;
+	case -1:  LOAD_RAMPS(f, f);     break;
+	default:  /* impossible */      break;
+	}
+    }
+}
+
+
+/**
+ * Restore all gamma ramps
+ */
+void restore_gamma(void)
+{
+  size_t i;
+  int gerror;
+  
+#define RESTORE_RAMPS(SUFFIX, MEMBER) \
+  do \
+    if (outputs[i].saved_ramps.MEMBER.red != NULL) \
+      { \
+	gerror = libgamma_crtc_set_gamma_ramps##SUFFIX(outputs[i].crtc, outputs[i].saved_ramps.MEMBER); \
+	if (gerror) \
+	    libgamma_perror(argv0, gerror); \
+      } \
+  while (0)
+  
+  for (i = 0; i < outputs_n; i++)
+    {
+      if (outputs[i].supported == LIBGAMMA_NO)
+	continue;
+      
+      switch (outputs[i].depth)
+	{
+	case 64:  RESTORE_RAMPS(64, u64);  break;
+	case 32:  RESTORE_RAMPS(32, u32);  break;
+	case 16:  RESTORE_RAMPS(16, u16);  break;
+	case  8:  RESTORE_RAMPS( 8, u8);   break;
+	case -2:  RESTORE_RAMPS(d, d);     break;
+	case -1:  RESTORE_RAMPS(f, f);     break;
+	default:  /* impossible */         break;
+	}
+    }
+}
+
+
+
+/**
+ * Disconnect from the site
+ * 
+ * @return  Zero on success, -1 on error
+ */
+int disconnect(void)
+{
+  if (!connected)
+    return 0;
+  
+  connected = 0;
+  return 0; /* TODO disconnect() */
+}
+
+
+/**
+ * Reconnect to the site
+ * 
+ * @return  Zero on success, -1 on error
+ */
+int reconnect(void)
+{
+  if (connected)
+    return 0;
+  
+  connected = 1;
+  return 0; /* TODO reconnect() */
+}
+
diff --git a/src/servers/gamma.h b/src/servers/gamma.h
new file mode 100644
index 0000000..ee9af84
--- /dev/null
+++ b/src/servers/gamma.h
@@ -0,0 +1,94 @@
+/**
+ * coopgammad -- Cooperative gamma server
+ * Copyright (C) 2016  Mattias Andrée (maandree@kth.se)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef SERVERS_GAMMA_H
+#define SERVERS_GAMMA_H
+
+
+#include "../types/output.h"
+
+#include <stddef.h>
+
+
+
+#ifndef GCC_ONLY
+# if defined(__GNUC__) && !defined(__clang__)
+#  define GCC_ONLY(...)  __VA_ARGS__
+# else
+#  define GCC_ONLY(...)  /* nothing */
+# endif
+#endif
+
+
+
+/**
+ * Handle a ‘Command: set-gamma’ message
+ * 
+ * @param   conn        The index of the connection
+ * @param   message_id  The value of the ‘Message ID’ header
+ * @param   crtc        The value of the ‘CRTC’ header
+ * @return              Zero on success (even if ignored), -1 on error,
+ *                      1 if connection closed
+ */
+GCC_ONLY(__attribute__((nonnull(2))))
+int handle_get_gamma_info(size_t conn, const char* restrict message_id, const char* restrict crtc);
+
+/**
+ * Set the gamma ramps on an output
+ * 
+ * @param  output  The output
+ * @param  ramps   The gamma ramps
+ */
+GCC_ONLY(__attribute__((nonnull)))
+void set_gamma(const struct output* restrict output, const union gamma_ramps* restrict ramps);
+
+
+/**
+ * Store all current gamma ramps
+ * 
+ * @return  Zero on success, -1 on error
+ */
+int initialise_gamma_info(void);
+
+/**
+ * Store all current gamma ramps
+ */
+void store_gamma(void);
+
+/**
+ * Restore all gamma ramps
+ */
+void restore_gamma(void);
+
+
+/**
+ * Disconnect from the site
+ * 
+ * @return  Zero on success, -1 on error
+ */
+int disconnect(void);
+
+/**
+ * Reconnect to the site
+ * 
+ * @return  Zero on success, -1 on error
+ */
+int reconnect(void);
+
+
+#endif
+
diff --git a/src/servers/kernel.c b/src/servers/kernel.c
new file mode 100644
index 0000000..ce3246a
--- /dev/null
+++ b/src/servers/kernel.c
@@ -0,0 +1,351 @@
+/**
+ * coopgammad -- Cooperative gamma server
+ * Copyright (C) 2016  Mattias Andrée (maandree@kth.se)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include "kernel.h"
+#include "../state.h"
+#include "../util.h"
+
+#include <libgamma.h>
+
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/un.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <pwd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+
+
+/**
+ * Get the pathname of the runtime file
+ * 
+ * @param   suffix  The suffix for the file
+ * @return          The pathname of the file, `NULL` on error
+ */
+GCC_ONLY(__attribute__((malloc, nonnull)))
+static char* get_pathname(const char* restrict suffix)
+{
+  const char* restrict rundir = getenv("XDG_RUNTIME_DIR");
+  const char* restrict username = "";
+  char* name = NULL;
+  char* p;
+  char* restrict rc;
+  struct passwd* restrict pw;
+  size_t n;
+  int saved_errno;
+  
+  if (site.site)
+    {
+      name = memdup(site.site, strlen(site.site) + 1);
+      if (name == NULL)
+	goto fail;
+    }
+  else if ((name = libgamma_method_default_site(site.method)))
+    {
+      name = memdup(name, strlen(name) + 1);
+      if (name == NULL)
+	goto fail;
+    }
+  
+  if (name != NULL)
+    switch (site.method)
+      {
+      case LIBGAMMA_METHOD_X_RANDR:
+      case LIBGAMMA_METHOD_X_VIDMODE:
+	if ((p = strrchr(name, ':')))
+	  if ((p = strchr(p, '.')))
+	    *p = '\0';
+	break;
+      default:
+	break;
+      }
+  
+  if (!rundir || !*rundir)
+    rundir = "/tmp";
+  
+  if ((pw = getpwuid(getuid())))
+    username = pw->pw_name ? pw->pw_name : "";
+  
+  n = sizeof("/.coopgammad/~/.") + 3 * sizeof(int);
+  n += strlen(rundir) + strlen(username) + strlen(name) + strlen(suffix);
+  if (!(rc = malloc(n)))
+    goto fail;
+  sprintf(rc, "%s/.coopgammad/~%s/%i%s%s%s",
+	  rundir, username, site.method, name ? "." : "", name ? name : "", suffix);
+  return rc;
+  
+ fail:
+  saved_errno = errno;
+  free(name);
+  errno = saved_errno;
+  return NULL;
+}
+
+
+/**
+ * Get the pathname of the socket
+ * 
+ * @return  The pathname of the socket, `NULL` on error
+ */
+char* get_socket_pathname(void)
+{
+  return get_pathname(".socket");
+}
+
+
+/**
+ * Get the pathname of the PID file
+ * 
+ * @return  The pathname of the PID file, `NULL` on error
+ */
+char* get_pidfile_pathname(void)
+{
+  return get_pathname(".pid");
+}
+
+
+/**
+ * Get the pathname of the state file
+ * 
+ * @return  The pathname of the state file, `NULL` on error
+ */
+char* get_state_pathname(void)
+{
+  return get_pathname(".state");
+}
+
+
+/**
+ * Check whether a PID file is outdated
+ * 
+ * @param   pidpath  The PID file
+ * @param   token    An environment variable (including both key and value)
+ *                   that must exist in the process if it is a coopgammad process
+ * @return           -1: An error occurred
+ *                    0: The service is already running
+ *                    1: The PID file is outdated
+ */
+GCC_ONLY(__attribute__((nonnull)))
+static int is_pidfile_reusable(const char* restrict pidpath, const char* restrict token)
+{
+  /* PORTERS: /proc/$PID/environ is Linux specific */
+  
+  char temp[sizeof("/proc//environ") + 3 * sizeof(pid_t)];
+  int fd = -1, saved_errno, tries = 0;
+  char* content = NULL;
+  char* p;
+  pid_t pid = 0;
+  size_t n;
+#if defined(HAVE_LINUX_PROCFS)
+  char* end;
+#else
+  (void) token;
+#endif
+  
+  /* Get PID */
+ retry:
+  fd = open(pidpath, O_RDONLY);
+  if (fd < 0)
+    return -1;
+  content = nread(fd, &n);
+  if (content == NULL)
+    goto fail;
+  close(fd), fd = -1;
+  
+  if (n == 0)
+    {
+      if (++tries > 1)
+	goto bad;
+      msleep(100); /* 1 tenth of a second */
+      goto retry;
+    }
+  
+  if (('0' > content[0]) || (content[0] > '9'))
+    goto bad;
+  if ((content[0] == '0') && ('0' <= content[1]) && (content[1] <= '9'))
+    goto bad;
+  for (p = content; *p; p++)
+    if (('0' <= *p) && (*p <= '9'))
+      pid = pid * 10 + (*p & 15);
+    else
+      break;
+  if (*p++ != '\n')
+    goto bad;
+  if (*p)
+    goto bad;
+  if ((size_t)(content - p) != n)
+    goto bad;
+  sprintf(temp, "%llu", (unsigned long long)pid);
+  if (strcmp(content, temp))
+    goto bad;
+  
+  /* Validate PID */
+#if defined(HAVE_LINUX_PROCFS)
+  sprintf(temp, "/proc/%llu/environ", (unsigned long long)pid);
+  fd = open(temp, O_RDONLY);
+  if (fd < 0)
+    return ((errno == ENOENT) || (errno == EACCES)) ? 1 : -1;
+  content = nread(fd, &n);
+  if (content == NULL)
+    goto fail;
+  close(fd), fd = -1;
+  
+  for (end = (p = content) + n; p != end; p = strchr(p, '\0') + 1)
+    if (!strcmp(p, token))
+      return 0;
+#else
+  if ((kill(pid, 0) == 0) || (errno == EINVAL))
+    return 0;
+#endif
+  
+  return 1;
+ bad:
+  fprintf(stderr, "%s: pid file contain invalid content: %s\n", argv0, pidpath);
+  errno = 0;
+  return -1;
+ fail:
+  saved_errno = errno;
+  free(content);
+  if (fd >= 0)
+    close(fd);
+  errno = saved_errno;
+  return -1;
+}
+
+
+/**
+ * Create PID file
+ * 
+ * @param   pidpath  The pathname of the PID file
+ * @return           Zero on success, -1 on error,
+ *                   -2 if the service is already running
+ */
+int create_pidfile(char* pidpath)
+{
+  int fd, r, saved_errno;
+  char* p;
+  char* restrict token;
+  
+  /* Create token used to validate the service. */
+  token = malloc(sizeof("COOPGAMMAD_PIDFILE_TOKEN=") + strlen(pidpath));
+  if (token == NULL)
+    return -1;
+  sprintf(token, "COOPGAMMAD_PIDFILE_TOKEN=%s", pidpath);
+  if (putenv(token))
+    return -1;
+  
+  /* Create PID file's directory. */
+  for (p = pidpath; *p == '/'; p++);
+  while ((p = strchr(p, '/')))
+    {
+      *p = '\0';
+      if (mkdir(pidpath, 0644) < 0)
+	if (errno != EEXIST)
+	  return -1;
+      *p++ = '/';
+    }
+  
+  /* Create PID file. */
+ retry:
+  fd = open(pidpath, O_CREAT | O_EXCL, 0644);
+  if (fd < 0)
+    {
+      if (errno == EINTR)
+	goto retry;
+      if (errno != EEXIST)
+	return -1;
+      r = is_pidfile_reusable(pidpath, token);
+      if (r > 0)
+	{
+	  unlink(pidpath);
+	  goto retry;
+	}
+      else if (r < 0)
+	goto fail;
+      fprintf(stderr, "%s: service is already running\n", argv0);
+      errno = 0;
+      return -2;
+    }
+  
+  /* Write PID to PID file. */
+  if (dprintf(fd, "%llu\n", (unsigned long long)getpid()) < 0)
+    goto fail;
+  
+  /* Done */
+  if (close(fd) < 0)
+    if (errno != EINTR)
+      return -1;
+  return 0;
+ fail:
+  saved_errno = errno;
+  close(fd);
+  unlink(pidpath);
+  errno = saved_errno;
+  return -1;
+}
+
+
+/**
+ * Create socket and start listening
+ * 
+ * @param   socketpath  The pathname of the socket
+ * @return              Zero on success, -1 on error
+ */
+int create_socket(const char* socketpath)
+{
+  struct sockaddr_un address;
+  
+  address.sun_family = AF_UNIX;
+  if (strlen(socketpath) >= sizeof(address.sun_path))
+    {
+      errno = ENAMETOOLONG;
+      return -1;
+    }
+  strcpy(address.sun_path, socketpath);
+  unlink(socketpath);
+  if ((socketfd = socket(PF_UNIX, SOCK_STREAM, 0)) < 0)
+    return -1;
+  if (fchmod(socketfd, S_IRWXU) < 0)
+    return -1;
+  if (bind(socketfd, (struct sockaddr*)(&address), (socklen_t)sizeof(address)) < 0)
+    return -1;
+  if (listen(socketfd, SOMAXCONN) < 0)
+    return -1;
+  
+  return 0;
+}
+
+
+/**
+ * Close and unlink the socket
+ * 
+ * @param  socketpath  The pathname of the socket
+ */
+void close_socket(const char* socketpath)
+{
+  if (socketfd >= 0)
+    {
+      shutdown(socketfd, SHUT_RDWR);
+      close(socketfd);
+      unlink(socketpath);
+    }
+}
+
diff --git a/src/servers/kernel.h b/src/servers/kernel.h
new file mode 100644
index 0000000..494e150
--- /dev/null
+++ b/src/servers/kernel.h
@@ -0,0 +1,85 @@
+/**
+ * coopgammad -- Cooperative gamma server
+ * Copyright (C) 2016  Mattias Andrée (maandree@kth.se)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef SERVERS_KERNEL_H
+#define SERVERS_KERNEL_H
+
+
+#ifndef GCC_ONLY
+# if defined(__GNUC__) && !defined(__clang__)
+#  define GCC_ONLY(...)  __VA_ARGS__
+# else
+#  define GCC_ONLY(...)  /* nothing */
+# endif
+#endif
+
+
+
+/**
+ * Get the pathname of the socket
+ * 
+ * @return  The pathname of the socket, `NULL` on error
+ */
+GCC_ONLY(__attribute__((malloc)))
+char* get_socket_pathname(void);
+
+/**
+ * Get the pathname of the PID file
+ * 
+ * @return  The pathname of the PID file, `NULL` on error
+ */
+GCC_ONLY(__attribute__((malloc)))
+char* get_pidfile_pathname(void);
+
+/**
+ * Get the pathname of the state file
+ * 
+ * @return  The pathname of the state file, `NULL` on error
+ */
+GCC_ONLY(__attribute__((malloc)))
+char* get_state_pathname(void);
+
+/**
+ * Create PID file
+ * 
+ * @param   pidpath  The pathname of the PID file
+ * @return           Zero on success, -1 on error,
+ *                   -2 if the service is already running
+ */
+GCC_ONLY(__attribute__((nonnull)))
+int create_pidfile(char* pidpath);
+
+/**
+ * Create socket and start listening
+ * 
+ * @param   socketpath  The pathname of the socket
+ * @return              Zero on success, -1 on error
+ */
+GCC_ONLY(__attribute__((nonnull)))
+int create_socket(const char* socketpath);
+
+/**
+ * Close and unlink the socket
+ * 
+ * @param  socketpath  The pathname of the socket
+ */
+GCC_ONLY(__attribute__((nonnull)))
+void close_socket(const char* socketpath);
+
+
+#endif
+