1 files changed, 75 insertions, 0 deletions
diff --git a/src/unistd/preadn.c b/src/unistd/preadn.c
new file mode 100644
index 0000000..d7da108
--- /dev/null
+++ b/src/unistd/preadn.c
@@ -0,0 +1,75 @@
+/**
+ * slibc — Yet another C library
+ * Copyright © 2015  Mattias Andrée (maandree@member.fsf.org)
+ * 
+ * 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 <unistd.h>
+#include <signal.h>
+
+
+
+/**
+ * Variant of `pread` that will read until the request
+ * amount of that has been read, or there is no more
+ * data to read. This function will block signals so
+ * that it cannot throw `EINTR`, which could mean that
+ * read data is lost. Note however, it may fail for
+ * any other reason resulting in lost data.
+ * 
+ * This is a slibc extension.
+ * 
+ * @etymology  Variant of `(pread)` that reads all `(n)byte` bytes!
+ * 
+ * @param  fd      The file descriptor whence the data shall be read.
+ * @param  buf     The buffer whither the read data shall be stored.
+ * @param  nbyte   The number of bytes to read.
+ * @param  offset  Whence in the file the read begins.
+ * 
+ * @throws  Any error specified for pread(3), except `EINTR`.
+ * 
+ * @since  Always.
+ */
+ssize_t preadn(int fd, void* buf, size_t nbyte, off_t offset)
+{
+  char *buffer = buf;
+  ssize_t r, n = 0;
+  sigset_t mask, oldmask;
+  int saved_errno = 0;
+  
+  sigfillset(&mask);
+  sigprocmask(SIG_BLOCK, &mask, &oldmask);
+  
+  while (nbyte)
+    {
+      r = pread(fildes, buffer, nbyte, offset);
+      if (r < 0)
+	goto fail;
+      if (r == 0)
+	break;
+      n += r;
+      nbyte -= (size_t)r;
+      offset += (off_t)r;
+      buffer += r;
+    }
+
+  sigprocmask(SIG_SETMASK, &oldmask, NULL);
+  return n;
+ fail:
+  errno = saved_errno;
+  sigprocmask(SIG_SETMASK, &oldmask, NULL);
+  saved_errno = errno;
+  return -1;
+}
+