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