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                         if (lock_file_list->fd >= 0)
  17                                 close(lock_file_list->fd);
  18                         unlink(lock_file_list->filename);
  19                 }
  20                 lock_file_list = lock_file_list->next;
  21         }
  22 }
  23
  24 static void remove_lock_file_on_signal(int signo)
  25 {
  26         remove_lock_file();
  27         signal(signo, SIG_DFL);
  28         raise(signo);
  29 }
  30
  31 /*
  32  * p = absolute or relative path name
  33  *
  34  * Return a pointer into p showing the beginning of the last path name
  35  * element.  If p is empty or the root directory ("/"), just return p.
  36  */
  37 static char *last_path_elm(char *p)
  38 {
  39         /* r starts pointing to null at the end of the string */
  40         char *r = strchr(p, '\0');
  41
  42         if (r == p)
  43                 return p; /* just return empty string */
  44
  45         r--; /* back up to last non-null character */
  46
  47         /* back up past trailing slashes, if any */
  48         while (r > p && *r == '/')
  49                 r--;
  50
  51         /*
  52          * then go backwards until I hit a slash, or the beginning of
  53          * the string
  54          */
  55         while (r > p && *(r-1) != '/')
  56                 r--;
  57         return r;
  58 }
  59
  60
  61 /* We allow "recursive" symbolic links. Only within reason, though */
  62 #define MAXDEPTH 5
  63
  64 /*
  65  * p = path that may be a symlink
  66  * s = full size of p
  67  *
  68  * If p is a symlink, attempt to overwrite p with a path to the real
  69  * file or directory (which may or may not exist), following a chain of
  70  * symlinks if necessary.  Otherwise, leave p unmodified.
  71  *
  72  * This is a best-effort routine.  If an error occurs, p will either be
  73  * left unmodified or will name a different symlink in a symlink chain
  74  * that started with p's initial contents.
  75  *
  76  * Always returns p.
  77  */
  78
  79 static char *resolve_symlink(char *p, size_t s)
  80 {
  81         int depth = MAXDEPTH;
  82
  83         while (depth--) {
  84                 char link[PATH_MAX];
  85                 int link_len = readlink(p, link, sizeof(link));
  86                 if (link_len < 0) {
  87                         /* not a symlink anymore */
  88                         return p;
  89                 }
  90                 else if (link_len < sizeof(link))
  91                         /* readlink() never null-terminates */
  92                         link[link_len] = '\0';
  93                 else {
  94                         warning("%s: symlink too long", p);
  95                         return p;
  96                 }
  97
  98                 if (is_absolute_path(link)) {
  99                         /* absolute path simply replaces p */
 100                         if (link_len < s)
 101                                 strcpy(p, link);
 102                         else {
 103                                 warning("%s: symlink too long", p);
 104                                 return p;
 105                         }
 106                 } else {
 107                         /*
 108                          * link is a relative path, so I must replace the
 109                          * last element of p with it.
 110                          */
 111                         char *r = (char*)last_path_elm(p);
 112                         if (r - p + link_len < s)
 113                                 strcpy(r, link);
 114                         else {
 115                                 warning("%s: symlink too long", p);
 116                                 return p;
 117                         }
 118                 }
 119         }
 120         return p;
 121 }
 122
 123
 124 static int lock_file(struct lock_file *lk, const char *path)
 125 {
 126         if (strlen(path) >= sizeof(lk->filename)) return -1;
 127         strcpy(lk->filename, path);
 128         /*
 129          * subtract 5 from size to make sure there's room for adding
 130          * ".lock" for the lock file name
 131          */
 132         resolve_symlink(lk->filename, sizeof(lk->filename)-5);
 133         strcat(lk->filename, ".lock");
 134         lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
 135         if (0 <= lk->fd) {
 136                 if (!lock_file_list) {
 137                         signal(SIGINT, remove_lock_file_on_signal);
 138                         signal(SIGHUP, remove_lock_file_on_signal);
 139                         signal(SIGTERM, remove_lock_file_on_signal);
 140                         signal(SIGQUIT, 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 int hold_lock_file_for_update(struct lock_file *lk, const char *path, int die_on_error)
 159 {
 160         int fd = lock_file(lk, path);
 161         if (fd < 0 && die_on_error)
 162                 die("unable to create '%s.lock': %s", path, strerror(errno));
 163         return fd;
 164 }
 165
 166 int hold_lock_file_for_append(struct lock_file *lk, const char *path, int die_on_error)
 167 {
 168         int fd, orig_fd;
 169
 170         fd = lock_file(lk, path);
 171         if (fd < 0) {
 172                 if (die_on_error)
 173                         die("unable to create '%s.lock': %s", path, strerror(errno));
 174                 return fd;
 175         }
 176
 177         orig_fd = open(path, O_RDONLY);
 178         if (orig_fd < 0) {
 179                 if (errno != ENOENT) {
 180                         if (die_on_error)
 181                                 die("cannot open '%s' for copying", path);
 182                         close(fd);
 183                         return error("cannot open '%s' for copying", path);
 184                 }
 185         } else if (copy_fd(orig_fd, fd)) {
 186                 if (die_on_error)
 187                         exit(128);
 188                 close(fd);
 189                 return -1;
 190         }
 191         return fd;
 192 }
 193
 194 int close_lock_file(struct lock_file *lk)
 195 {
 196         int fd = lk->fd;
 197         lk->fd = -1;
 198         return close(fd);
 199 }
 200
 201 int commit_lock_file(struct lock_file *lk)
 202 {
 203         char result_file[PATH_MAX];
 204         size_t i;
 205         if (lk->fd >= 0 && close_lock_file(lk))
 206                 return -1;
 207         strcpy(result_file, lk->filename);
 208         i = strlen(result_file) - 5; /* .lock */
 209         result_file[i] = 0;
 210         if (rename(lk->filename, result_file))
 211                 return -1;
 212         lk->filename[0] = 0;
 213         return 0;
 214 }
 215
 216 int hold_locked_index(struct lock_file *lk, int die_on_error)
 217 {
 218         return hold_lock_file_for_update(lk, get_index_file(), die_on_error);
 219 }
 220
 221 void set_alternate_index_output(const char *name)
 222 {
 223         alternate_index_output = name;
 224 }
 225
 226 int commit_locked_index(struct lock_file *lk)
 227 {
 228         if (alternate_index_output) {
 229                 if (lk->fd >= 0 && close_lock_file(lk))
 230                         return -1;
 231                 if (rename(lk->filename, alternate_index_output))
 232                         return -1;
 233                 lk->filename[0] = 0;
 234                 return 0;
 235         }
 236         else
 237                 return commit_lock_file(lk);
 238 }
 239
 240 void rollback_lock_file(struct lock_file *lk)
 241 {
 242         if (lk->filename[0]) {
 243                 if (lk->fd >= 0)
 244                         close(lk->fd);
 245                 unlink(lk->filename);
 246         }
 247         lk->filename[0] = 0;
 248 }