/**
* 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);
pthread_sigmask(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;
}
pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
return n;
fail:
errno = saved_errno;
pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
saved_errno = errno;
return -1;
}
