lockfile.c

   1 /*
   2  * Copyright (c) 2005, Junio C Hamano
   3  */
   4 #include "cache.h"
   5 #include "sigchain.h"
   6
   7 static struct lock_file *lock_file_list;
   8 static const char *alternate_index_output;
   9
  10 static void remove_lock_file(void)
  11 {
  12         pid_t me = getpid();
  13
  14         while (lock_file_list) {
  15                 if (lock_file_list->owner == me &&
  16                     lock_file_list->filename[0]) {
  17                         if (lock_file_list->fd >= 0)
  18                                 close(lock_file_list->fd);
  19                         unlink(lock_file_list->filename);
  20                 }
  21                 lock_file_list = lock_file_list->next;
  22         }
  23 }
  24
  25 static void remove_lock_file_on_signal(int signo)
  26 {
  27         remove_lock_file();
  28         sigchain_pop(signo);
  29         raise(signo);
  30 }
  31
  32 /*
  33  * p = absolute or relative path name
  34  *
  35  * Return a pointer into p showing the beginning of the last path name
  36  * element.  If p is empty or the root directory ("/"), just return p.
  37  */
  38 static char *last_path_elm(char *p)
  39 {
  40         /* r starts pointing to null at the end of the string */
  41         char *r = strchr(p, '\0');
  42
  43         if (r == p)
  44                 return p; /* just return empty string */
  45
  46         r--; /* back up to last non-null character */
  47
  48         /* back up past trailing slashes, if any */
  49         while (r > p && *r == '/')
  50                 r--;
  51
  52         /*
  53          * then go backwards until I hit a slash, or the beginning of
  54          * the string
  55          */
  56         while (r > p && *(r-1) != '/')
  57                 r--;
  58         return r;
  59 }
  60
  61
  62 /* We allow "recursive" symbolic links. Only within reason, though */
  63 #define MAXDEPTH 5
  64
  65 /*
  66  * p = path that may be a symlink
  67  * s = full size of p
  68  *
  69  * If p is a symlink, attempt to overwrite p with a path to the real
  70  * file or directory (which may or may not exist), following a chain of
  71  * symlinks if necessary.  Otherwise, leave p unmodified.
  72  *
  73  * This is a best-effort routine.  If an error occurs, p will either be
  74  * left unmodified or will name a different symlink in a symlink chain
  75  * that started with p's initial contents.
  76  *
  77  * Always returns p.
  78  */
  79
  80 static char *resolve_symlink(char *p, size_t s)
  81 {
  82         int depth = MAXDEPTH;
  83
  84         while (depth--) {
  85                 char link[PATH_MAX];
  86                 int link_len = readlink(p, link, sizeof(link));
  87                 if (link_len < 0) {
  88                         /* not a symlink anymore */
  89                         return p;
  90                 }
  91                 else if (link_len < sizeof(link))
  92                         /* readlink() never null-terminates */
  93                         link[link_len] = '\0';
  94                 else {
  95                         warning("%s: symlink too long", p);
  96                         return p;
  97                 }
  98
  99                 if (is_absolute_path(link)) {
 100                         /* absolute path simply replaces p */
 101                         if (link_len < s)
 102                                 strcpy(p, link);
 103                         else {
 104                                 warning("%s: symlink too long", p);
 105                                 return p;
 106                         }
 107                 } else {
 108                         /*
 109                          * link is a relative path, so I must replace the
 110                          * last element of p with it.
 111                          */
 112                         char *r = (char*)last_path_elm(p);
 113                         if (r - p + link_len < s)
 114                                 strcpy(r, link);
 115                         else {
 116                                 warning("%s: symlink too long", p);
 117                                 return p;
 118                         }
 119                 }
 120         }
 121         return p;
 122 }
 123
 124
 125 static int lock_file(struct lock_file *lk, const char *path, int flags)
 126 {
 127         if (strlen(path) >= sizeof(lk->filename))
 128                 return -1;
 129         strcpy(lk->filename, path);
 130         /*
 131          * subtract 5 from size to make sure there's room for adding
 132          * ".lock" for the lock file name
 133          */
 134         if (!(flags & LOCK_NODEREF))
 135                 resolve_symlink(lk->filename, sizeof(lk->filename)-5);
 136         strcat(lk->filename, ".lock");
 137         lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
 138         if (0 <= lk->fd) {
 139                 if (!lock_file_list) {
 140                         sigchain_push_common(remove_lock_file_on_signal);
 141                         atexit(remove_lock_file);
 142                 }
 143                 lk->owner = getpid();
 144                 if (!lk->on_list) {
 145                         lk->next = lock_file_list;
 146                         lock_file_list = lk;
 147                         lk->on_list = 1;
 148                 }
 149                 if (adjust_shared_perm(lk->filename))
 150                         return error("cannot fix permission bits on %s",
 151                                      lk->filename);
 152         }
 153         else
 154                 lk->filename[0] = 0;
 155         return lk->fd;
 156 }
 157
 158
 159 NORETURN void unable_to_lock_index_die(const char *path, int err)
 160 {
 161         if (err == EEXIST) {
 162                 die("Unable to create '%s.lock': %s.\n\n"
 163                     "If no other git process is currently running, this probably means a\n"
 164                     "git process crashed in this repository earlier. Make sure no other git\n"
 165                     "process is running and remove the file manually to continue.",
 166                     path, strerror(err));
 167         } else {
 168                 die("Unable to create '%s.lock': %s", path, strerror(err));
 169         }
 170 }
 171
 172 int hold_lock_file_for_update(struct lock_file *lk, const char *path, int flags)
 173 {
 174         int fd = lock_file(lk, path, flags);
 175         if (fd < 0 && (flags & LOCK_DIE_ON_ERROR))
 176                 unable_to_lock_index_die(path, errno);
 177         return fd;
 178 }
 179
 180 int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
 181 {
 182         int fd, orig_fd;
 183
 184         fd = lock_file(lk, path, flags);
 185         if (fd < 0) {
 186                 if (flags & LOCK_DIE_ON_ERROR)
 187                         unable_to_lock_index_die(path, errno);
 188                 return fd;
 189         }
 190
 191         orig_fd = open(path, O_RDONLY);
 192         if (orig_fd < 0) {
 193                 if (errno != ENOENT) {
 194                         if (flags & LOCK_DIE_ON_ERROR)
 195                                 die("cannot open '%s' for copying", path);
 196                         close(fd);
 197                         return error("cannot open '%s' for copying", path);
 198                 }
 199         } else if (copy_fd(orig_fd, fd)) {
 200                 if (flags & LOCK_DIE_ON_ERROR)
 201                         exit(128);
 202                 close(fd);
 203                 return -1;
 204         }
 205         return fd;
 206 }
 207
 208 int close_lock_file(struct lock_file *lk)
 209 {
 210         int fd = lk->fd;
 211         lk->fd = -1;
 212         return close(fd);
 213 }
 214
 215 int commit_lock_file(struct lock_file *lk)
 216 {
 217         char result_file[PATH_MAX];
 218         size_t i;
 219         if (lk->fd >= 0 && close_lock_file(lk))
 220                 return -1;
 221         strcpy(result_file, lk->filename);
 222         i = strlen(result_file) - 5; /* .lock */
 223         result_file[i] = 0;
 224         if (rename(lk->filename, result_file))
 225                 return -1;
 226         lk->filename[0] = 0;
 227         return 0;
 228 }
 229
 230 int hold_locked_index(struct lock_file *lk, int die_on_error)
 231 {
 232         return hold_lock_file_for_update(lk, get_index_file(),
 233                                          die_on_error
 234                                          ? LOCK_DIE_ON_ERROR
 235                                          : 0);
 236 }
 237
 238 void set_alternate_index_output(const char *name)
 239 {
 240         alternate_index_output = name;
 241 }
 242
 243 int commit_locked_index(struct lock_file *lk)
 244 {
 245         if (alternate_index_output) {
 246                 if (lk->fd >= 0 && close_lock_file(lk))
 247                         return -1;
 248                 if (rename(lk->filename, alternate_index_output))
 249                         return -1;
 250                 lk->filename[0] = 0;
 251                 return 0;
 252         }
 253         else
 254                 return commit_lock_file(lk);
 255 }
 256
 257 void rollback_lock_file(struct lock_file *lk)
 258 {
 259         if (lk->filename[0]) {
 260                 if (lk->fd >= 0)
 261                         close(lk->fd);
 262                 unlink(lk->filename);
 263         }
 264         lk->filename[0] = 0;
 265 }