lockfile.c

   1 /*
   2  * Copyright (c) 2005, Junio C Hamano
   3  */
   4 #include "cache.h"
   5
   6 static struct lock_file *lock_file_list;
   7 static const char *alternate_index_output;
   8
   9 static void remove_lock_file(void)
  10 {
  11         pid_t me = getpid();
  12
  13         while (lock_file_list) {
  14                 if (lock_file_list->owner == me &&
  15                     lock_file_list->filename[0]) {
  16                         close(lock_file_list->fd);
  17                         unlink(lock_file_list->filename);
  18                 }
  19                 lock_file_list = lock_file_list->next;
  20         }
  21 }
  22
  23 static void remove_lock_file_on_signal(int signo)
  24 {
  25         remove_lock_file();
  26         signal(SIGINT, SIG_DFL);
  27         raise(signo);
  28 }
  29
  30 /*
  31  * p = absolute or relative path name
  32  *
  33  * Return a pointer into p showing the beginning of the last path name
  34  * element.  If p is empty or the root directory ("/"), just return p.
  35  */
  36 static char *last_path_elm(char *p)
  37 {
  38         /* r starts pointing to null at the end of the string */
  39         char *r = strchr(p, '\0');
  40
  41         if (r == p)
  42                 return p; /* just return empty string */
  43
  44         r--; /* back up to last non-null character */
  45
  46         /* back up past trailing slashes, if any */
  47         while (r > p && *r == '/')
  48                 r--;
  49
  50         /*
  51          * then go backwards until I hit a slash, or the beginning of
  52          * the string
  53          */
  54         while (r > p && *(r-1) != '/')
  55                 r--;
  56         return r;
  57 }
  58
  59
  60 /* We allow "recursive" symbolic links. Only within reason, though */
  61 #define MAXDEPTH 5
  62
  63 /*
  64  * p = path that may be a symlink
  65  * s = full size of p
  66  *
  67  * If p is a symlink, attempt to overwrite p with a path to the real
  68  * file or directory (which may or may not exist), following a chain of
  69  * symlinks if necessary.  Otherwise, leave p unmodified.
  70  *
  71  * This is a best-effort routine.  If an error occurs, p will either be
  72  * left unmodified or will name a different symlink in a symlink chain
  73  * that started with p's initial contents.
  74  *
  75  * Always returns p.
  76  */
  77
  78 static char *resolve_symlink(char *p, size_t s)
  79 {
  80         int depth = MAXDEPTH;
  81
  82         while (depth--) {
  83                 char link[PATH_MAX];
  84                 int link_len = readlink(p, link, sizeof(link));
  85                 if (link_len < 0) {
  86                         /* not a symlink anymore */
  87                         return p;
  88                 }
  89                 else if (link_len < sizeof(link))
  90                         /* readlink() never null-terminates */
  91                         link[link_len] = '\0';
  92                 else {
  93                         warning("%s: symlink too long", p);
  94                         return p;
  95                 }
  96
  97                 if (link[0] == '/') {
  98                         /* absolute path simply replaces p */
  99                         if (link_len < s)
 100                                 strcpy(p, link);
 101                         else {
 102                                 warning("%s: symlink too long", p);
 103                                 return p;
 104                         }
 105                 } else {
 106                         /*
 107                          * link is a relative path, so I must replace the
 108                          * last element of p with it.
 109                          */
 110                         char *r = (char*)last_path_elm(p);
 111                         if (r - p + link_len < s)
 112                                 strcpy(r, link);
 113                         else {
 114                                 warning("%s: symlink too long", p);
 115                                 return p;
 116                         }
 117                 }
 118         }
 119         return p;
 120 }
 121
 122
 123 static int lock_file(struct lock_file *lk, const char *path)
 124 {
 125         if (strlen(path) >= sizeof(lk->filename)) return -1;
 126         strcpy(lk->filename, path);
 127         /*
 128          * subtract 5 from size to make sure there's room for adding
 129          * ".lock" for the lock file name
 130          */
 131         resolve_symlink(lk->filename, sizeof(lk->filename)-5);
 132         strcat(lk->filename, ".lock");
 133         lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
 134         if (0 <= lk->fd) {
 135                 if (!lock_file_list) {
 136                         signal(SIGINT, remove_lock_file_on_signal);
 137                         atexit(remove_lock_file);
 138                 }
 139                 lk->owner = getpid();
 140                 if (!lk->on_list) {
 141                         lk->next = lock_file_list;
 142                         lock_file_list = lk;
 143                         lk->on_list = 1;
 144                 }
 145                 if (adjust_shared_perm(lk->filename))
 146                         return error("cannot fix permission bits on %s",
 147                                      lk->filename);
 148         }
 149         else
 150                 lk->filename[0] = 0;
 151         return lk->fd;
 152 }
 153
 154 int hold_lock_file_for_update(struct lock_file *lk, const char *path, int die_on_error)
 155 {
 156         int fd = lock_file(lk, path);
 157         if (fd < 0 && die_on_error)
 158                 die("unable to create '%s.lock': %s", path, strerror(errno));
 159         return fd;
 160 }
 161
 162 int commit_lock_file(struct lock_file *lk)
 163 {
 164         char result_file[PATH_MAX];
 165         int i;
 166         close(lk->fd);
 167         strcpy(result_file, lk->filename);
 168         i = strlen(result_file) - 5; /* .lock */
 169         result_file[i] = 0;
 170         i = rename(lk->filename, result_file);
 171         lk->filename[0] = 0;
 172         return i;
 173 }
 174
 175 int hold_locked_index(struct lock_file *lk, int die_on_error)
 176 {
 177         return hold_lock_file_for_update(lk, get_index_file(), die_on_error);
 178 }
 179
 180 void set_alternate_index_output(const char *name)
 181 {
 182         alternate_index_output = name;
 183 }
 184
 185 int commit_locked_index(struct lock_file *lk)
 186 {
 187         if (alternate_index_output) {
 188                 int result = rename(lk->filename, alternate_index_output);
 189                 lk->filename[0] = 0;
 190                 return result;
 191         }
 192         else
 193                 return commit_lock_file(lk);
 194 }
 195
 196 void rollback_lock_file(struct lock_file *lk)
 197 {
 198         if (lk->filename[0]) {
 199                 close(lk->fd);
 200                 unlink(lk->filename);
 201         }
 202         lk->filename[0] = 0;
 203 }