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/* Create /proc/self/fd-related names for subfiles of open directories.
Copyright (C) 2006, 2009-2015 Free Software Foundation, Inc.
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/>. */
/* Written by Paul Eggert. */
#include <config.h>
#include "openat-priv.h"
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "intprops.h"
#define PROC_SELF_FD_FORMAT "/proc/self/fd/%d/%s"
#define PROC_SELF_FD_NAME_SIZE_BOUND(len) \
(sizeof PROC_SELF_FD_FORMAT - sizeof "%d%s" \
+ INT_STRLEN_BOUND (int) + (len) + 1)
/* Set BUF to the expansion of PROC_SELF_FD_FORMAT, using FD and FILE
respectively for %d and %s. If successful, return BUF if the
result fits in BUF, dynamically allocated memory otherwise. But
return NULL if /proc is not reliable, either because the operating
system support is lacking or because memory is low. */
char *
openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file)
{
static int proc_status = 0;
/* Make sure the caller gets ENOENT when appropriate. */
if (!*file)
{
buf[0] = '\0';
return buf;
}
if (! proc_status)
{
/* Set PROC_STATUS to a positive value if /proc/self/fd is
reliable, and a negative value otherwise. Solaris 10
/proc/self/fd mishandles "..", and any file name might expand
to ".." after symbolic link expansion, so avoid /proc/self/fd
if it mishandles "..". Solaris 10 has openat, but this
problem is exhibited on code that built on Solaris 8 and
running on Solaris 10. */
int proc_self_fd = open ("/proc/self/fd",
O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NONBLOCK);
if (proc_self_fd < 0)
proc_status = -1;
else
{
/* Detect whether /proc/self/fd/%i/../fd exists, where %i is the
number of a file descriptor open on /proc/self/fd. On Linux,
that name resolves to /proc/self/fd, which was opened above.
However, on Solaris, it may resolve to /proc/self/fd/fd, which
cannot exist, since all names in /proc/self/fd are numeric. */
char dotdot_buf[PROC_SELF_FD_NAME_SIZE_BOUND (sizeof "../fd" - 1)];
sprintf (dotdot_buf, PROC_SELF_FD_FORMAT, proc_self_fd, "../fd");
proc_status = access (dotdot_buf, F_OK) ? -1 : 1;
close (proc_self_fd);
}
}
if (proc_status < 0)
return NULL;
else
{
size_t bufsize = PROC_SELF_FD_NAME_SIZE_BOUND (strlen (file));
char *result = buf;
if (OPENAT_BUFFER_SIZE < bufsize)
{
result = malloc (bufsize);
if (! result)
return NULL;
}
sprintf (result, PROC_SELF_FD_FORMAT, fd, file);
return result;
}
}
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