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 <sys/stat.h>
  18
  19 #include <errno.h>
  20 #include <fcntl.h>
  21 #include <stdlib.h>
  22 #include <unistd.h>
  23 #include <string.h>
  24 #include <stdio.h>
  25 #include <time.h>
  26
  27 #include "got_error.h"
  28 #include "got_path.h"
  29
  30 #include "got_lib_lockfile.h"
  31
  32 const struct got_error *
  33 got_lockfile_lock(struct got_lockfile **lf, const char *path, int dir_fd)
  34 {
  35         const struct got_error *err = NULL;
  36         int attempts = 5;
  37
  38         *lf = calloc(1, sizeof(**lf));
  39         if (*lf == NULL)
  40                 return got_error_from_errno("calloc");
  41         (*lf)->fd = -1;
  42
  43         (*lf)->locked_path = strdup(path);
  44         if ((*lf)->locked_path == NULL) {
  45                 err = got_error_from_errno("strdup");
  46                 goto done;
  47         }
  48
  49         if (asprintf(&(*lf)->path, "%s%s", path, GOT_LOCKFILE_SUFFIX) == -1) {
  50                 err = got_error_from_errno("asprintf");
  51                 goto done;
  52         }
  53
  54         do {
  55                 if (dir_fd != -1) {
  56                         (*lf)->fd = openat(dir_fd, (*lf)->path,
  57                             O_RDONLY | O_CREAT | O_EXCL | O_EXLOCK | O_CLOEXEC,
  58                             GOT_DEFAULT_FILE_MODE);
  59                 } else {
  60                         (*lf)->fd = open((*lf)->path,
  61                             O_RDONLY | O_CREAT | O_EXCL | O_EXLOCK | O_CLOEXEC,
  62                             GOT_DEFAULT_FILE_MODE);
  63                 }
  64                 if ((*lf)->fd != -1)
  65                         break;
  66                 if (errno != EEXIST) {
  67                         err = got_error_from_errno2("open", (*lf)->path);
  68                         goto done;
  69                 }
  70                 sleep(1);
  71         } while (--attempts > 0);
  72
  73         if ((*lf)->fd == -1)
  74                 err = got_error(GOT_ERR_LOCKFILE_TIMEOUT);
  75 done:
  76         if (err) {
  77                 got_lockfile_unlock(*lf, dir_fd);
  78                 *lf = NULL;
  79         }
  80         return err;
  81 }
  82
  83 const struct got_error *
  84 got_lockfile_unlock(struct got_lockfile *lf, int dir_fd)
  85 {
  86         const struct got_error *err = NULL;
  87
  88         if (dir_fd != -1) {
  89                 if (lf->path && lf->fd != -1 &&
  90                     unlinkat(dir_fd, lf->path, 0) != 0)
  91                         err = got_error_from_errno("unlinkat");
  92         } else if (lf->path && lf->fd != -1 && unlink(lf->path) != 0)
  93                 err = got_error_from_errno("unlink");
  94         if (lf->fd != -1 && close(lf->fd) == -1 && err == NULL)
  95                 err = got_error_from_errno("close");
  96         free(lf->path);
  97         free(lf->locked_path);
  98         free(lf);
  99         return err;
 100 }