tempfile.c

   1 /*
   2  * State diagram and cleanup
   3  * -------------------------
   4  *
   5  * If the program exits while a temporary file is active, we want to
   6  * make sure that we remove it. This is done by remembering the active
   7  * temporary files in a linked list, `tempfile_list`. An `atexit(3)`
   8  * handler and a signal handler are registered, to clean up any active
   9  * temporary files.
  10  *
  11  * Because the signal handler can run at any time, `tempfile_list` and
  12  * the `tempfile` objects that comprise it must be kept in
  13  * self-consistent states at all times.
  14  *
  15  * The possible states of a `tempfile` object are as follows:
  16  *
  17  * - Uninitialized. In this state the object's `on_list` field must be
  18  *   zero but the rest of its contents need not be initialized. As
  19  *   soon as the object is used in any way, it is irrevocably
  20  *   registered in `tempfile_list`, and `on_list` is set.
  21  *
  22  * - Active, file open (after `create_tempfile()` or
  23  *   `reopen_tempfile()`). In this state:
  24  *
  25  *   - the temporary file exists
  26  *   - `active` is set
  27  *   - `filename` holds the filename of the temporary file
  28  *   - `fd` holds a file descriptor open for writing to it
  29  *   - `fp` holds a pointer to an open `FILE` object if and only if
  30  *     `fdopen_tempfile()` has been called on the object
  31  *   - `owner` holds the PID of the process that created the file
  32  *
  33  * - Active, file closed (after `close_tempfile_gently()`). Same
  34  *   as the previous state, except that the temporary file is closed,
  35  *   `fd` is -1, and `fp` is `NULL`.
  36  *
  37  * - Inactive (after `delete_tempfile()`, `rename_tempfile()`, or a
  38  *   failed attempt to create a temporary file). In this state:
  39  *
  40  *   - `active` is unset
  41  *   - `filename` is empty (usually, though there are transitory
  42  *     states in which this condition doesn't hold). Client code should
  43  *     *not* rely on the filename being empty in this state.
  44  *   - `fd` is -1 and `fp` is `NULL`
  45  *   - the object is left registered in the `tempfile_list`, and
  46  *     `on_list` is set.
  47  *
  48  * A temporary file is owned by the process that created it. The
  49  * `tempfile` has an `owner` field that records the owner's PID. This
  50  * field is used to prevent a forked process from deleting a temporary
  51  * file created by its parent.
  52  */
  53
  54 #include "cache.h"
  55 #include "tempfile.h"
  56 #include "sigchain.h"
  57
  58 static struct tempfile *volatile tempfile_list;
  59
  60 static void remove_tempfiles(int skip_fclose)
  61 {
  62         pid_t me = getpid();
  63
  64         while (tempfile_list) {
  65                 if (tempfile_list->owner == me) {
  66                         /* fclose() is not safe to call in a signal handler */
  67                         if (skip_fclose)
  68                                 tempfile_list->fp = NULL;
  69                         delete_tempfile(tempfile_list);
  70                 }
  71                 tempfile_list = tempfile_list->next;
  72         }
  73 }
  74
  75 static void remove_tempfiles_on_exit(void)
  76 {
  77         remove_tempfiles(0);
  78 }
  79
  80 static void remove_tempfiles_on_signal(int signo)
  81 {
  82         remove_tempfiles(1);
  83         sigchain_pop(signo);
  84         raise(signo);
  85 }
  86
  87 /*
  88  * Initialize *tempfile if necessary and add it to tempfile_list.
  89  */
  90 static void prepare_tempfile_object(struct tempfile *tempfile)
  91 {
  92         if (!tempfile_list) {
  93                 /* One-time initialization */
  94                 sigchain_push_common(remove_tempfiles_on_signal);
  95                 atexit(remove_tempfiles_on_exit);
  96         }
  97
  98         if (is_tempfile_active(tempfile))
  99                 BUG("prepare_tempfile_object called for active object");
 100         if (!tempfile->on_list) {
 101                 /* Initialize *tempfile and add it to tempfile_list: */
 102                 tempfile->fd = -1;
 103                 tempfile->fp = NULL;
 104                 tempfile->active = 0;
 105                 tempfile->owner = 0;
 106                 strbuf_init(&tempfile->filename, 0);
 107                 tempfile->next = tempfile_list;
 108                 tempfile_list = tempfile;
 109                 tempfile->on_list = 1;
 110         } else if (tempfile->filename.len) {
 111                 /* This shouldn't happen, but better safe than sorry. */
 112                 BUG("prepare_tempfile_object called for improperly-reset object");
 113         }
 114 }
 115
 116 static void activate_tempfile(struct tempfile *tempfile)
 117 {
 118         tempfile->owner = getpid();
 119         tempfile->active = 1;
 120 }
 121
 122 /* Make sure errno contains a meaningful value on error */
 123 int create_tempfile(struct tempfile *tempfile, const char *path)
 124 {
 125         prepare_tempfile_object(tempfile);
 126
 127         strbuf_add_absolute_path(&tempfile->filename, path);
 128         tempfile->fd = open(tempfile->filename.buf,
 129                             O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, 0666);
 130         if (O_CLOEXEC && tempfile->fd < 0 && errno == EINVAL)
 131                 /* Try again w/o O_CLOEXEC: the kernel might not support it */
 132                 tempfile->fd = open(tempfile->filename.buf,
 133                                     O_RDWR | O_CREAT | O_EXCL, 0666);
 134         if (tempfile->fd < 0) {
 135                 strbuf_reset(&tempfile->filename);
 136                 return -1;
 137         }
 138         activate_tempfile(tempfile);
 139         if (adjust_shared_perm(tempfile->filename.buf)) {
 140                 int save_errno = errno;
 141                 error("cannot fix permission bits on %s", tempfile->filename.buf);
 142                 delete_tempfile(tempfile);
 143                 errno = save_errno;
 144                 return -1;
 145         }
 146         return tempfile->fd;
 147 }
 148
 149 void register_tempfile(struct tempfile *tempfile, const char *path)
 150 {
 151         prepare_tempfile_object(tempfile);
 152         strbuf_add_absolute_path(&tempfile->filename, path);
 153         activate_tempfile(tempfile);
 154 }
 155
 156 int mks_tempfile_sm(struct tempfile *tempfile,
 157                     const char *template, int suffixlen, int mode)
 158 {
 159         prepare_tempfile_object(tempfile);
 160
 161         strbuf_add_absolute_path(&tempfile->filename, template);
 162         tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
 163         if (tempfile->fd < 0) {
 164                 strbuf_reset(&tempfile->filename);
 165                 return -1;
 166         }
 167         activate_tempfile(tempfile);
 168         return tempfile->fd;
 169 }
 170
 171 int mks_tempfile_tsm(struct tempfile *tempfile,
 172                      const char *template, int suffixlen, int mode)
 173 {
 174         const char *tmpdir;
 175
 176         prepare_tempfile_object(tempfile);
 177
 178         tmpdir = getenv("TMPDIR");
 179         if (!tmpdir)
 180                 tmpdir = "/tmp";
 181
 182         strbuf_addf(&tempfile->filename, "%s/%s", tmpdir, template);
 183         tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
 184         if (tempfile->fd < 0) {
 185                 strbuf_reset(&tempfile->filename);
 186                 return -1;
 187         }
 188         activate_tempfile(tempfile);
 189         return tempfile->fd;
 190 }
 191
 192 int xmks_tempfile_m(struct tempfile *tempfile, const char *template, int mode)
 193 {
 194         int fd;
 195         struct strbuf full_template = STRBUF_INIT;
 196
 197         strbuf_add_absolute_path(&full_template, template);
 198         fd = mks_tempfile_m(tempfile, full_template.buf, mode);
 199         if (fd < 0)
 200                 die_errno("Unable to create temporary file '%s'",
 201                           full_template.buf);
 202
 203         strbuf_release(&full_template);
 204         return fd;
 205 }
 206
 207 FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode)
 208 {
 209         if (!is_tempfile_active(tempfile))
 210                 BUG("fdopen_tempfile() called for inactive object");
 211         if (tempfile->fp)
 212                 BUG("fdopen_tempfile() called for open object");
 213
 214         tempfile->fp = fdopen(tempfile->fd, mode);
 215         return tempfile->fp;
 216 }
 217
 218 const char *get_tempfile_path(struct tempfile *tempfile)
 219 {
 220         if (!is_tempfile_active(tempfile))
 221                 BUG("get_tempfile_path() called for inactive object");
 222         return tempfile->filename.buf;
 223 }
 224
 225 int get_tempfile_fd(struct tempfile *tempfile)
 226 {
 227         if (!is_tempfile_active(tempfile))
 228                 BUG("get_tempfile_fd() called for inactive object");
 229         return tempfile->fd;
 230 }
 231
 232 FILE *get_tempfile_fp(struct tempfile *tempfile)
 233 {
 234         if (!is_tempfile_active(tempfile))
 235                 BUG("get_tempfile_fp() called for inactive object");
 236         return tempfile->fp;
 237 }
 238
 239 int close_tempfile_gently(struct tempfile *tempfile)
 240 {
 241         int fd;
 242         FILE *fp;
 243         int err;
 244
 245         if (!is_tempfile_active(tempfile) || tempfile->fd < 0)
 246                 return 0;
 247
 248         fd = tempfile->fd;
 249         fp = tempfile->fp;
 250         tempfile->fd = -1;
 251         if (fp) {
 252                 tempfile->fp = NULL;
 253                 if (ferror(fp)) {
 254                         err = -1;
 255                         if (!fclose(fp))
 256                                 errno = EIO;
 257                 } else {
 258                         err = fclose(fp);
 259                 }
 260         } else {
 261                 err = close(fd);
 262         }
 263
 264         return err ? -1 : 0;
 265 }
 266
 267 int reopen_tempfile(struct tempfile *tempfile)
 268 {
 269         if (!is_tempfile_active(tempfile))
 270                 BUG("reopen_tempfile called for an inactive object");
 271         if (0 <= tempfile->fd)
 272                 BUG("reopen_tempfile called for an open object");
 273         tempfile->fd = open(tempfile->filename.buf, O_WRONLY);
 274         return tempfile->fd;
 275 }
 276
 277 int rename_tempfile(struct tempfile *tempfile, const char *path)
 278 {
 279         if (!is_tempfile_active(tempfile))
 280                 BUG("rename_tempfile called for inactive object");
 281
 282         if (close_tempfile_gently(tempfile)) {
 283                 delete_tempfile(tempfile);
 284                 return -1;
 285         }
 286
 287         if (rename(tempfile->filename.buf, path)) {
 288                 int save_errno = errno;
 289                 delete_tempfile(tempfile);
 290                 errno = save_errno;
 291                 return -1;
 292         }
 293
 294         tempfile->active = 0;
 295         strbuf_reset(&tempfile->filename);
 296         return 0;
 297 }
 298
 299 void delete_tempfile(struct tempfile *tempfile)
 300 {
 301         if (!is_tempfile_active(tempfile))
 302                 return;
 303
 304         close_tempfile_gently(tempfile);
 305         unlink_or_warn(tempfile->filename.buf);
 306         tempfile->active = 0;
 307         strbuf_reset(&tempfile->filename);
 308 }