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e7190fc73d
This interface allows to obtain the associated process ID from the
process file descriptor. It is done by parsing the procps fdinfo
information. Its prototype is:
pid_t pidfd_getpid (int fd)
It returns the associated pid or -1 in case of an error and sets the
errno accordingly. The possible errno values are those from open, read,
and close (used on procps parsing), along with:
- EBADF if the FD is negative, does not have a PID associated, or if
the fdinfo fields contain a value larger than pid_t.
- EREMOTE if the PID is in a separate namespace.
- ESRCH if the process is already terminated.
Checked on x86_64-linux-gnu on Linux 4.15 (no CLONE_PIDFD or waitid
support), Linux 5.4 (full support), and Linux 6.2.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
127 lines
3.2 KiB
C
127 lines
3.2 KiB
C
/* pidfd_getpid - Get the associated pid from the pid file descriptor.
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Copyright (C) 2023 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <_itoa.h>
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#include <errno.h>
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#include <intprops.h>
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#include <procutils.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sysdep.h>
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#include <unistd.h>
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#define FDINFO_TO_FILENAME_PREFIX "/proc/self/fdinfo/"
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#define FDINFO_FILENAME_LEN \
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(sizeof (FDINFO_TO_FILENAME_PREFIX) + INT_STRLEN_BOUND (int))
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struct parse_fdinfo_t
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{
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bool found;
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pid_t pid;
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};
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/* Parse the PID field in the fdinfo entry, if existent. Avoid strtol or
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similar to not be locale dependent. */
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static int
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parse_fdinfo (const char *l, void *arg)
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{
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enum { fieldlen = sizeof ("Pid:") - 1 };
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if (strncmp (l, "Pid:", fieldlen) != 0)
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return 0;
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l += fieldlen;
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/* Skip leading spaces. */
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while (*l == ' ' || (unsigned int) (*l) -'\t' < 5)
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l++;
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bool neg = false;
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switch (*l)
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{
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case '-':
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neg = true;
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l++;
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break;
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case '+':
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return -1;
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}
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if (*l == '\0')
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return 0;
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int n = 0;
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while (*l != '\0')
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{
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/* Check if '*l' is a digit. */
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if ('0' > *l || *l > '9')
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return -1;
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/* Ignore invalid large values. */
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if (INT_MULTIPLY_WRAPV (10, n, &n)
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|| INT_ADD_WRAPV (n, *l++ - '0', &n))
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return -1;
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}
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/* -1 indicates that the process is terminated. */
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if (neg && n != 1)
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return -1;
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struct parse_fdinfo_t *fdinfo = arg;
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fdinfo->pid = neg ? -n : n;
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fdinfo->found = true;
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return 1;
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}
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pid_t
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pidfd_getpid (int fd)
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{
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if (__glibc_unlikely (fd < 0))
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{
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__set_errno (EBADF);
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return -1;
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}
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char fdinfoname[FDINFO_FILENAME_LEN];
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char *p = mempcpy (fdinfoname, FDINFO_TO_FILENAME_PREFIX,
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strlen (FDINFO_TO_FILENAME_PREFIX));
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*_fitoa_word (fd, p, 10, 0) = '\0';
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struct parse_fdinfo_t fdinfo = { .found = false, .pid = -1 };
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if (!procutils_read_file (fdinfoname, parse_fdinfo, &fdinfo))
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/* The fdinfo contains an invalid 'Pid:' value. */
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return INLINE_SYSCALL_ERROR_RETURN_VALUE (EBADF);
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/* The FD does not have a 'Pid:' entry associated. */
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if (!fdinfo.found)
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return INLINE_SYSCALL_ERROR_RETURN_VALUE (EBADF);
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/* The pidfd cannot be resolved because it is in a separate pid
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namespace. */
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if (fdinfo.pid == 0)
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return INLINE_SYSCALL_ERROR_RETURN_VALUE (EREMOTE);
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/* A negative value means the process is terminated. */
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if (fdinfo.pid < 0)
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return INLINE_SYSCALL_ERROR_RETURN_VALUE (ESRCH);
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return fdinfo.pid;
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}
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