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/* Return a range of open file descriptors.
Copyright (C) 2021-2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <errno.h>
#include <fcntl.h>
#include <support/support.h>
#include <support/check.h>
#include <support/xunistd.h>
#include <stdlib.h>
#include <sys/resource.h>
static void
increase_nofile (void)
{
struct rlimit rl;
if (getrlimit (RLIMIT_NOFILE, &rl) == -1)
FAIL_EXIT1 ("getrlimit (RLIMIT_NOFILE): %m");
rl.rlim_cur += 128;
if (setrlimit (RLIMIT_NOFILE, &rl) == 1)
FAIL_EXIT1 ("setrlimit (RLIMIT_NOFILE): %m");
}
static int
open_dev_null (int flags, mode_t mode)
{
int fd = open64 ("/dev/null", flags, mode);
if (fd >= 0)
return fd;
if (fd < 0 && errno != EMFILE)
FAIL_EXIT1 ("open64 (\"/dev/null\", 0x%x, 0%o): %m", flags, mode);
increase_nofile ();
return xopen ("/dev/null", flags, mode);
}
struct range
{
int lowfd;
size_t len;
};
struct range_list
{
size_t total;
size_t used;
struct range *ranges;
};
static void
range_init (struct range_list *r)
{
r->total = 8;
r->used = 0;
r->ranges = xmalloc (r->total * sizeof (struct range));
}
static void
range_add (struct range_list *r, int lowfd, size_t len)
{
if (r->used == r->total)
{
r->total *= 2;
r->ranges = xrealloc (r->ranges, r->total * sizeof (struct range));
}
r->ranges[r->used].lowfd = lowfd;
r->ranges[r->used].len = len;
r->used++;
}
static void
range_close (struct range_list *r)
{
for (size_t i = 0; i < r->used; i++)
{
int minfd = r->ranges[i].lowfd;
int maxfd = r->ranges[i].lowfd + r->ranges[i].len;
for (int fd = minfd; fd < maxfd; fd++)
xclose (fd);
}
free (r->ranges);
}
int
support_open_dev_null_range (int num, int flags, mode_t mode)
{
/* We keep track of the ranges that hit an already opened descriptor, so
we close them after we get a working range. */
struct range_list rl;
range_init (&rl);
int lowfd = open_dev_null (flags, mode);
int prevfd = lowfd;
while (true)
{
int i = 1;
for (; i < num; i++)
{
int fd = open_dev_null (flags, mode);
if (fd != lowfd + i)
{
range_add (&rl, lowfd, prevfd - lowfd + 1);
prevfd = lowfd = fd;
break;
}
prevfd = fd;
}
if (i == num)
break;
}
range_close (&rl);
return lowfd;
}
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