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 successful `close_tempfile()`). 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()`, a
  38  *   failed attempt to create a temporary file, or a failed
  39  *   `close_tempfile()`). In this state:
  40  *
  41  *   - `active` is unset
  42  *   - `filename` is empty (usually, though there are transitory
  43  *     states in which this condition doesn't hold). Client code should
  44  *     *not* rely on the filename being empty in this state.
  45  *   - `fd` is -1 and `fp` is `NULL`
  46  *   - the object is left registered in the `tempfile_list`, and
  47  *     `on_list` is set.
  48  *
  49  * A temporary file is owned by the process that created it. The
  50  * `tempfile` has an `owner` field that records the owner's PID. This
  51  * field is used to prevent a forked process from deleting a temporary
  52  * file created by its parent.
  53  */
  54
  55 #include "cache.h"
  56 #include "tempfile.h"
  57 #include "sigchain.h"
  58
  59 static struct tempfile *volatile tempfile_list;
  60
  61 static void remove_tempfiles(int skip_fclose)
  62 {
  63         pid_t me = getpid();
  64
  65         while (tempfile_list) {
  66                 if (tempfile_list->owner == me) {
  67                         /* fclose() is not safe to call in a signal handler */
  68                         if (skip_fclose)
  69                                 tempfile_list->fp = NULL;
  70                         delete_tempfile(tempfile_list);
  71                 }
  72                 tempfile_list = tempfile_list->next;
  73         }
  74 }
  75
  76 static void remove_tempfiles_on_exit(void)
  77 {
  78         remove_tempfiles(0);
  79 }
  80
  81 static void remove_tempfiles_on_signal(int signo)
  82 {
  83         remove_tempfiles(1);
  84         sigchain_pop(signo);
  85         raise(signo);
  86 }
  87
  88 /*
  89  * Initialize *tempfile if necessary and add it to tempfile_list.
  90  */
  91 static void prepare_tempfile_object(struct tempfile *tempfile)
  92 {
  93         if (!tempfile_list) {
  94                 /* One-time initialization */
  95                 sigchain_push_common(remove_tempfiles_on_signal);
  96                 atexit(remove_tempfiles_on_exit);
  97         }
  98
  99         if (tempfile->active)
 100                 die("BUG: prepare_tempfile_object called for active object");
 101         if (!tempfile->on_list) {
 102                 /* Initialize *tempfile and add it to tempfile_list: */
 103                 tempfile->fd = -1;
 104                 tempfile->fp = NULL;
 105                 tempfile->active = 0;
 106                 tempfile->owner = 0;
 107                 strbuf_init(&tempfile->filename, 0);
 108                 tempfile->next = tempfile_list;
 109                 tempfile_list = tempfile;
 110                 tempfile->on_list = 1;
 111         } else if (tempfile->filename.len) {
 112                 /* This shouldn't happen, but better safe than sorry. */
 113                 die("BUG: prepare_tempfile_object called for improperly-reset object");
 114         }
 115 }
 116
 117 /* Make sure errno contains a meaningful value on error */
 118 int create_tempfile(struct tempfile *tempfile, const char *path)
 119 {
 120         prepare_tempfile_object(tempfile);
 121
 122         strbuf_add_absolute_path(&tempfile->filename, path);
 123         tempfile->fd = open(tempfile->filename.buf, O_RDWR | O_CREAT | O_EXCL, 0666);
 124         if (tempfile->fd < 0) {
 125                 strbuf_reset(&tempfile->filename);
 126                 return -1;
 127         }
 128         tempfile->owner = getpid();
 129         tempfile->active = 1;
 130         if (adjust_shared_perm(tempfile->filename.buf)) {
 131                 int save_errno = errno;
 132                 error("cannot fix permission bits on %s", tempfile->filename.buf);
 133                 delete_tempfile(tempfile);
 134                 errno = save_errno;
 135                 return -1;
 136         }
 137         return tempfile->fd;
 138 }
 139
 140 void register_tempfile(struct tempfile *tempfile, const char *path)
 141 {
 142         prepare_tempfile_object(tempfile);
 143         strbuf_add_absolute_path(&tempfile->filename, path);
 144         tempfile->owner = getpid();
 145         tempfile->active = 1;
 146 }
 147
 148 int mks_tempfile_sm(struct tempfile *tempfile,
 149                     const char *template, int suffixlen, int mode)
 150 {
 151         prepare_tempfile_object(tempfile);
 152
 153         strbuf_add_absolute_path(&tempfile->filename, template);
 154         tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
 155         if (tempfile->fd < 0) {
 156                 strbuf_reset(&tempfile->filename);
 157                 return -1;
 158         }
 159         tempfile->owner = getpid();
 160         tempfile->active = 1;
 161         return tempfile->fd;
 162 }
 163
 164 int mks_tempfile_tsm(struct tempfile *tempfile,
 165                      const char *template, int suffixlen, int mode)
 166 {
 167         const char *tmpdir;
 168
 169         prepare_tempfile_object(tempfile);
 170
 171         tmpdir = getenv("TMPDIR");
 172         if (!tmpdir)
 173                 tmpdir = "/tmp";
 174
 175         strbuf_addf(&tempfile->filename, "%s/%s", tmpdir, template);
 176         tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
 177         if (tempfile->fd < 0) {
 178                 strbuf_reset(&tempfile->filename);
 179                 return -1;
 180         }
 181         tempfile->owner = getpid();
 182         tempfile->active = 1;
 183         return tempfile->fd;
 184 }
 185
 186 int xmks_tempfile_m(struct tempfile *tempfile, const char *template, int mode)
 187 {
 188         int fd;
 189         struct strbuf full_template = STRBUF_INIT;
 190
 191         strbuf_add_absolute_path(&full_template, template);
 192         fd = mks_tempfile_m(tempfile, full_template.buf, mode);
 193         if (fd < 0)
 194                 die_errno("Unable to create temporary file '%s'",
 195                           full_template.buf);
 196
 197         strbuf_release(&full_template);
 198         return fd;
 199 }
 200
 201 FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode)
 202 {
 203         if (!tempfile->active)
 204                 die("BUG: fdopen_tempfile() called for inactive object");
 205         if (tempfile->fp)
 206                 die("BUG: fdopen_tempfile() called for open object");
 207
 208         tempfile->fp = fdopen(tempfile->fd, mode);
 209         return tempfile->fp;
 210 }
 211
 212 const char *get_tempfile_path(struct tempfile *tempfile)
 213 {
 214         if (!tempfile->active)
 215                 die("BUG: get_tempfile_path() called for inactive object");
 216         return tempfile->filename.buf;
 217 }
 218
 219 int get_tempfile_fd(struct tempfile *tempfile)
 220 {
 221         if (!tempfile->active)
 222                 die("BUG: get_tempfile_fd() called for inactive object");
 223         return tempfile->fd;
 224 }
 225
 226 FILE *get_tempfile_fp(struct tempfile *tempfile)
 227 {
 228         if (!tempfile->active)
 229                 die("BUG: get_tempfile_fp() called for inactive object");
 230         return tempfile->fp;
 231 }
 232
 233 int close_tempfile(struct tempfile *tempfile)
 234 {
 235         int fd = tempfile->fd;
 236         FILE *fp = tempfile->fp;
 237         int err;
 238
 239         if (fd < 0)
 240                 return 0;
 241
 242         tempfile->fd = -1;
 243         if (fp) {
 244                 tempfile->fp = NULL;
 245
 246                 /*
 247                  * Note: no short-circuiting here; we want to fclose()
 248                  * in any case!
 249                  */
 250                 err = ferror(fp) | fclose(fp);
 251         } else {
 252                 err = close(fd);
 253         }
 254
 255         if (err) {
 256                 int save_errno = errno;
 257                 delete_tempfile(tempfile);
 258                 errno = save_errno;
 259                 return -1;
 260         }
 261
 262         return 0;
 263 }
 264
 265 int reopen_tempfile(struct tempfile *tempfile)
 266 {
 267         if (0 <= tempfile->fd)
 268                 die("BUG: reopen_tempfile called for an open object");
 269         if (!tempfile->active)
 270                 die("BUG: reopen_tempfile called for an inactive object");
 271         tempfile->fd = open(tempfile->filename.buf, O_WRONLY);
 272         return tempfile->fd;
 273 }
 274
 275 int rename_tempfile(struct tempfile *tempfile, const char *path)
 276 {
 277         if (!tempfile->active)
 278                 die("BUG: rename_tempfile called for inactive object");
 279
 280         if (close_tempfile(tempfile))
 281                 return -1;
 282
 283         if (rename(tempfile->filename.buf, path)) {
 284                 int save_errno = errno;
 285                 delete_tempfile(tempfile);
 286                 errno = save_errno;
 287                 return -1;
 288         }
 289
 290         tempfile->active = 0;
 291         strbuf_reset(&tempfile->filename);
 292         return 0;
 293 }
 294
 295 void delete_tempfile(struct tempfile *tempfile)
 296 {
 297         if (!tempfile->active)
 298                 return;
 299
 300         if (!close_tempfile(tempfile)) {
 301                 unlink_or_warn(tempfile->filename.buf);
 302                 tempfile->active = 0;
 303                 strbuf_reset(&tempfile->filename);
 304         }
 305 }