lib/lockfile.c

   1 /*
   2  * Copyright (c) 2019 Stefan Sperling <stsp@openbsd.org>
   3  *
   4  * Permission to use, copy, modify, and distribute this software for any
   5  * purpose with or without fee is hereby granted, provided that the above
   6  * copyright notice and this permission notice appear in all copies.
   7  *
   8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  15  */
  16
  17 #include "got_compat.h"
  18
  19 #include <sys/stat.h>
  20 #include <sys/queue.h>
  21 #include <sys/tree.h>
  22
  23 #include <errno.h>
  24 #include <fcntl.h>
  25 #include <stdlib.h>
  26 #include <unistd.h>
  27 #include <string.h>
  28 #include <stdio.h>
  29 #include <time.h>
  30
  31 #include "got_error.h"
  32 #include "got_path.h"
  33
  34 #include "got_lib_lockfile.h"
  35
  36 const struct got_error *
  37 got_lockfile_lock(struct got_lockfile **lf, const char *path, int dir_fd)
  38 {
  39         const struct got_error *err = NULL;
  40         int attempts = 5;
  41
  42         *lf = calloc(1, sizeof(**lf));
  43         if (*lf == NULL)
  44                 return got_error_from_errno("calloc");
  45         (*lf)->fd = -1;
  46
  47         (*lf)->locked_path = strdup(path);
  48         if ((*lf)->locked_path == NULL) {
  49                 err = got_error_from_errno("strdup");
  50                 goto done;
  51         }
  52
  53         if (asprintf(&(*lf)->path, "%s%s", path, GOT_LOCKFILE_SUFFIX) == -1) {
  54                 err = got_error_from_errno("asprintf");
  55                 goto done;
  56         }
  57
  58         do {
  59                 if (dir_fd != -1) {
  60                         (*lf)->fd = openat(dir_fd, (*lf)->path,
  61                             O_RDWR | O_CREAT | O_EXCL | O_EXLOCK | O_CLOEXEC,
  62                             GOT_DEFAULT_FILE_MODE);
  63                 } else {
  64                         (*lf)->fd = open((*lf)->path,
  65                             O_RDWR | O_CREAT | O_EXCL | O_EXLOCK | O_CLOEXEC,
  66                             GOT_DEFAULT_FILE_MODE);
  67                 }
  68                 if ((*lf)->fd != -1)
  69                         break;
  70                 if (errno != EEXIST) {
  71                         err = got_error_from_errno2("open", (*lf)->path);
  72                         goto done;
  73                 }
  74                 sleep(1);
  75         } while (--attempts > 0);
  76
  77         if ((*lf)->fd == -1) {
  78                 err = got_error_fmt(GOT_ERR_LOCKFILE_TIMEOUT,
  79                     "%s", (*lf)->path);
  80         }
  81 done:
  82         if (err) {
  83                 got_lockfile_unlock(*lf, dir_fd);
  84                 *lf = NULL;
  85         }
  86         return err;
  87 }
  88
  89 const struct got_error *
  90 got_lockfile_unlock(struct got_lockfile *lf, int dir_fd)
  91 {
  92         const struct got_error *err = NULL;
  93
  94         if (dir_fd != -1) {
  95                 if (lf->path && lf->fd != -1 &&
  96                     unlinkat(dir_fd, lf->path, 0) != 0)
  97                         err = got_error_from_errno("unlinkat");
  98         } else if (lf->path && lf->fd != -1 && unlink(lf->path) != 0)
  99                 err = got_error_from_errno("unlink");
 100         if (lf->fd != -1 && close(lf->fd) == -1 && err == NULL)
 101                 err = got_error_from_errno("close");
 102         free(lf->path);
 103         free(lf->locked_path);
 104         free(lf);
 105         return err;
 106 }