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(SIGINT, 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                         atexit(remove_lock_file);
 139                 }
 140                 lk->owner = getpid();
 141                 if (!lk->on_list) {
 142                         lk->next = lock_file_list;
 143                         lock_file_list = lk;
 144                         lk->on_list = 1;
 145                 }
 146                 if (adjust_shared_perm(lk->filename))
 147                         return error("cannot fix permission bits on %s",
 148                                      lk->filename);
 149         }
 150         else
 151                 lk->filename[0] = 0;
 152         return lk->fd;
 153 }
 154
 155 int hold_lock_file_for_update(struct lock_file *lk, const char *path, int die_on_error)
 156 {
 157         int fd = lock_file(lk, path);
 158         if (fd < 0 && die_on_error)
 159                 die("unable to create '%s.lock': %s", path, strerror(errno));
 160         return fd;
 161 }
 162
 163 int close_lock_file(struct lock_file *lk)
 164 {
 165         int fd = lk->fd;
 166         lk->fd = -1;
 167         return close(fd);
 168 }
 169
 170 int commit_lock_file(struct lock_file *lk)
 171 {
 172         char result_file[PATH_MAX];
 173         size_t i;
 174         if (lk->fd >= 0 && close_lock_file(lk))
 175                 return -1;
 176         strcpy(result_file, lk->filename);
 177         i = strlen(result_file) - 5; /* .lock */
 178         result_file[i] = 0;
 179         if (rename(lk->filename, result_file))
 180                 return -1;
 181         lk->filename[0] = 0;
 182         return 0;
 183 }
 184
 185 int hold_locked_index(struct lock_file *lk, int die_on_error)
 186 {
 187         return hold_lock_file_for_update(lk, get_index_file(), die_on_error);
 188 }
 189
 190 void set_alternate_index_output(const char *name)
 191 {
 192         alternate_index_output = name;
 193 }
 194
 195 int commit_locked_index(struct lock_file *lk)
 196 {
 197         if (alternate_index_output) {
 198                 if (lk->fd >= 0 && close_lock_file(lk))
 199                         return -1;
 200                 if (rename(lk->filename, alternate_index_output))
 201                         return -1;
 202                 lk->filename[0] = 0;
 203                 return 0;
 204         }
 205         else
 206                 return commit_lock_file(lk);
 207 }
 208
 209 void rollback_lock_file(struct lock_file *lk)
 210 {
 211         if (lk->filename[0]) {
 212                 if (lk->fd >= 0)
 213                         close(lk->fd);
 214                 unlink(lk->filename);
 215         }
 216         lk->filename[0] = 0;
 217 }