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 removed from `tempfile_list` (but could be used again)
  46  *
  47  * A temporary file is owned by the process that created it. The
  48  * `tempfile` has an `owner` field that records the owner's PID. This
  49  * field is used to prevent a forked process from deleting a temporary
  50  * file created by its parent.
  51  */
  52
  53 #include "cache.h"
  54 #include "tempfile.h"
  55 #include "sigchain.h"
  56
  57 static VOLATILE_LIST_HEAD(tempfile_list);
  58
  59 static void remove_tempfiles(int in_signal_handler)
  60 {
  61         pid_t me = getpid();
  62         volatile struct volatile_list_head *pos;
  63
  64         list_for_each(pos, &tempfile_list) {
  65                 struct tempfile *p = list_entry(pos, struct tempfile, list);
  66
  67                 if (!is_tempfile_active(p) || p->owner != me)
  68                         continue;
  69
  70                 if (p->fd >= 0)
  71                         close(p->fd);
  72
  73                 if (in_signal_handler)
  74                         unlink(p->filename.buf);
  75                 else
  76                         unlink_or_warn(p->filename.buf);
  77
  78                 p->active = 0;
  79         }
  80 }
  81
  82 static void remove_tempfiles_on_exit(void)
  83 {
  84         remove_tempfiles(0);
  85 }
  86
  87 static void remove_tempfiles_on_signal(int signo)
  88 {
  89         remove_tempfiles(1);
  90         sigchain_pop(signo);
  91         raise(signo);
  92 }
  93
  94 static struct tempfile *new_tempfile(void)
  95 {
  96         struct tempfile *tempfile = xmalloc(sizeof(*tempfile));
  97         tempfile->fd = -1;
  98         tempfile->fp = NULL;
  99         tempfile->active = 0;
 100         tempfile->owner = 0;
 101         INIT_LIST_HEAD(&tempfile->list);
 102         strbuf_init(&tempfile->filename, 0);
 103         return tempfile;
 104 }
 105
 106 static void activate_tempfile(struct tempfile *tempfile)
 107 {
 108         static int initialized;
 109
 110         if (is_tempfile_active(tempfile))
 111                 BUG("activate_tempfile called for active object");
 112
 113         if (!initialized) {
 114                 sigchain_push_common(remove_tempfiles_on_signal);
 115                 atexit(remove_tempfiles_on_exit);
 116                 initialized = 1;
 117         }
 118
 119         volatile_list_add(&tempfile->list, &tempfile_list);
 120         tempfile->owner = getpid();
 121         tempfile->active = 1;
 122 }
 123
 124 static void deactivate_tempfile(struct tempfile *tempfile)
 125 {
 126         tempfile->active = 0;
 127         strbuf_release(&tempfile->filename);
 128         volatile_list_del(&tempfile->list);
 129         free(tempfile);
 130 }
 131
 132 /* Make sure errno contains a meaningful value on error */
 133 struct tempfile *create_tempfile(const char *path)
 134 {
 135         struct tempfile *tempfile = new_tempfile();
 136
 137         strbuf_add_absolute_path(&tempfile->filename, path);
 138         tempfile->fd = open(tempfile->filename.buf,
 139                             O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, 0666);
 140         if (O_CLOEXEC && tempfile->fd < 0 && errno == EINVAL)
 141                 /* Try again w/o O_CLOEXEC: the kernel might not support it */
 142                 tempfile->fd = open(tempfile->filename.buf,
 143                                     O_RDWR | O_CREAT | O_EXCL, 0666);
 144         if (tempfile->fd < 0) {
 145                 deactivate_tempfile(tempfile);
 146                 return NULL;
 147         }
 148         activate_tempfile(tempfile);
 149         if (adjust_shared_perm(tempfile->filename.buf)) {
 150                 int save_errno = errno;
 151                 error("cannot fix permission bits on %s", tempfile->filename.buf);
 152                 delete_tempfile(&tempfile);
 153                 errno = save_errno;
 154                 return NULL;
 155         }
 156
 157         return tempfile;
 158 }
 159
 160 struct tempfile *register_tempfile(const char *path)
 161 {
 162         struct tempfile *tempfile = new_tempfile();
 163         strbuf_add_absolute_path(&tempfile->filename, path);
 164         activate_tempfile(tempfile);
 165         return tempfile;
 166 }
 167
 168 struct tempfile *mks_tempfile_sm(const char *filename_template, int suffixlen, int mode)
 169 {
 170         struct tempfile *tempfile = new_tempfile();
 171
 172         strbuf_add_absolute_path(&tempfile->filename, filename_template);
 173         tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
 174         if (tempfile->fd < 0) {
 175                 deactivate_tempfile(tempfile);
 176                 return NULL;
 177         }
 178         activate_tempfile(tempfile);
 179         return tempfile;
 180 }
 181
 182 struct tempfile *mks_tempfile_tsm(const char *filename_template, int suffixlen, int mode)
 183 {
 184         struct tempfile *tempfile = new_tempfile();
 185         const char *tmpdir;
 186
 187         tmpdir = getenv("TMPDIR");
 188         if (!tmpdir)
 189                 tmpdir = "/tmp";
 190
 191         strbuf_addf(&tempfile->filename, "%s/%s", tmpdir, filename_template);
 192         tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
 193         if (tempfile->fd < 0) {
 194                 deactivate_tempfile(tempfile);
 195                 return NULL;
 196         }
 197         activate_tempfile(tempfile);
 198         return tempfile;
 199 }
 200
 201 struct tempfile *xmks_tempfile_m(const char *filename_template, int mode)
 202 {
 203         struct tempfile *tempfile;
 204         struct strbuf full_template = STRBUF_INIT;
 205
 206         strbuf_add_absolute_path(&full_template, filename_template);
 207         tempfile = mks_tempfile_m(full_template.buf, mode);
 208         if (!tempfile)
 209                 die_errno("Unable to create temporary file '%s'",
 210                           full_template.buf);
 211
 212         strbuf_release(&full_template);
 213         return tempfile;
 214 }
 215
 216 FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode)
 217 {
 218         if (!is_tempfile_active(tempfile))
 219                 BUG("fdopen_tempfile() called for inactive object");
 220         if (tempfile->fp)
 221                 BUG("fdopen_tempfile() called for open object");
 222
 223         tempfile->fp = fdopen(tempfile->fd, mode);
 224         return tempfile->fp;
 225 }
 226
 227 const char *get_tempfile_path(struct tempfile *tempfile)
 228 {
 229         if (!is_tempfile_active(tempfile))
 230                 BUG("get_tempfile_path() called for inactive object");
 231         return tempfile->filename.buf;
 232 }
 233
 234 int get_tempfile_fd(struct tempfile *tempfile)
 235 {
 236         if (!is_tempfile_active(tempfile))
 237                 BUG("get_tempfile_fd() called for inactive object");
 238         return tempfile->fd;
 239 }
 240
 241 FILE *get_tempfile_fp(struct tempfile *tempfile)
 242 {
 243         if (!is_tempfile_active(tempfile))
 244                 BUG("get_tempfile_fp() called for inactive object");
 245         return tempfile->fp;
 246 }
 247
 248 int close_tempfile_gently(struct tempfile *tempfile)
 249 {
 250         int fd;
 251         FILE *fp;
 252         int err;
 253
 254         if (!is_tempfile_active(tempfile) || tempfile->fd < 0)
 255                 return 0;
 256
 257         fd = tempfile->fd;
 258         fp = tempfile->fp;
 259         tempfile->fd = -1;
 260         if (fp) {
 261                 tempfile->fp = NULL;
 262                 if (ferror(fp)) {
 263                         err = -1;
 264                         if (!fclose(fp))
 265                                 errno = EIO;
 266                 } else {
 267                         err = fclose(fp);
 268                 }
 269         } else {
 270                 err = close(fd);
 271         }
 272
 273         return err ? -1 : 0;
 274 }
 275
 276 int reopen_tempfile(struct tempfile *tempfile)
 277 {
 278         if (!is_tempfile_active(tempfile))
 279                 BUG("reopen_tempfile called for an inactive object");
 280         if (0 <= tempfile->fd)
 281                 BUG("reopen_tempfile called for an open object");
 282         tempfile->fd = open(tempfile->filename.buf, O_WRONLY);
 283         return tempfile->fd;
 284 }
 285
 286 int rename_tempfile(struct tempfile **tempfile_p, const char *path)
 287 {
 288         struct tempfile *tempfile = *tempfile_p;
 289
 290         if (!is_tempfile_active(tempfile))
 291                 BUG("rename_tempfile called for inactive object");
 292
 293         if (close_tempfile_gently(tempfile)) {
 294                 delete_tempfile(tempfile_p);
 295                 return -1;
 296         }
 297
 298         if (rename(tempfile->filename.buf, path)) {
 299                 int save_errno = errno;
 300                 delete_tempfile(tempfile_p);
 301                 errno = save_errno;
 302                 return -1;
 303         }
 304
 305         deactivate_tempfile(tempfile);
 306         *tempfile_p = NULL;
 307         return 0;
 308 }
 309
 310 void delete_tempfile(struct tempfile **tempfile_p)
 311 {
 312         struct tempfile *tempfile = *tempfile_p;
 313
 314         if (!is_tempfile_active(tempfile))
 315                 return;
 316
 317         close_tempfile_gently(tempfile);
 318         unlink_or_warn(tempfile->filename.buf);
 319         deactivate_tempfile(tempfile);
 320         *tempfile_p = NULL;
 321 }