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 /* Make sure errno contains a meaningful value on error */
  89 int create_tempfile(struct tempfile *tempfile, const char *path)
  90 {
  91         size_t pathlen = strlen(path);
  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: create_tempfile 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, pathlen);
 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: create_tempfile called for improperly-reset object");
 114         }
 115
 116         strbuf_add_absolute_path(&tempfile->filename, path);
 117         tempfile->fd = open(tempfile->filename.buf, O_RDWR | O_CREAT | O_EXCL, 0666);
 118         if (tempfile->fd < 0) {
 119                 strbuf_reset(&tempfile->filename);
 120                 return -1;
 121         }
 122         tempfile->owner = getpid();
 123         tempfile->active = 1;
 124         if (adjust_shared_perm(tempfile->filename.buf)) {
 125                 int save_errno = errno;
 126                 error("cannot fix permission bits on %s", tempfile->filename.buf);
 127                 delete_tempfile(tempfile);
 128                 errno = save_errno;
 129                 return -1;
 130         }
 131         return tempfile->fd;
 132 }
 133
 134 FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode)
 135 {
 136         if (!tempfile->active)
 137                 die("BUG: fdopen_tempfile() called for inactive object");
 138         if (tempfile->fp)
 139                 die("BUG: fdopen_tempfile() called for open object");
 140
 141         tempfile->fp = fdopen(tempfile->fd, mode);
 142         return tempfile->fp;
 143 }
 144
 145 const char *get_tempfile_path(struct tempfile *tempfile)
 146 {
 147         if (!tempfile->active)
 148                 die("BUG: get_tempfile_path() called for inactive object");
 149         return tempfile->filename.buf;
 150 }
 151
 152 int get_tempfile_fd(struct tempfile *tempfile)
 153 {
 154         if (!tempfile->active)
 155                 die("BUG: get_tempfile_fd() called for inactive object");
 156         return tempfile->fd;
 157 }
 158
 159 FILE *get_tempfile_fp(struct tempfile *tempfile)
 160 {
 161         if (!tempfile->active)
 162                 die("BUG: get_tempfile_fp() called for inactive object");
 163         return tempfile->fp;
 164 }
 165
 166 int close_tempfile(struct tempfile *tempfile)
 167 {
 168         int fd = tempfile->fd;
 169         FILE *fp = tempfile->fp;
 170         int err;
 171
 172         if (fd < 0)
 173                 return 0;
 174
 175         tempfile->fd = -1;
 176         if (fp) {
 177                 tempfile->fp = NULL;
 178
 179                 /*
 180                  * Note: no short-circuiting here; we want to fclose()
 181                  * in any case!
 182                  */
 183                 err = ferror(fp) | fclose(fp);
 184         } else {
 185                 err = close(fd);
 186         }
 187
 188         if (err) {
 189                 int save_errno = errno;
 190                 delete_tempfile(tempfile);
 191                 errno = save_errno;
 192                 return -1;
 193         }
 194
 195         return 0;
 196 }
 197
 198 int reopen_tempfile(struct tempfile *tempfile)
 199 {
 200         if (0 <= tempfile->fd)
 201                 die("BUG: reopen_tempfile called for an open object");
 202         if (!tempfile->active)
 203                 die("BUG: reopen_tempfile called for an inactive object");
 204         tempfile->fd = open(tempfile->filename.buf, O_WRONLY);
 205         return tempfile->fd;
 206 }
 207
 208 int rename_tempfile(struct tempfile *tempfile, const char *path)
 209 {
 210         if (!tempfile->active)
 211                 die("BUG: rename_tempfile called for inactive object");
 212
 213         if (close_tempfile(tempfile))
 214                 return -1;
 215
 216         if (rename(tempfile->filename.buf, path)) {
 217                 int save_errno = errno;
 218                 delete_tempfile(tempfile);
 219                 errno = save_errno;
 220                 return -1;
 221         }
 222
 223         tempfile->active = 0;
 224         strbuf_reset(&tempfile->filename);
 225         return 0;
 226 }
 227
 228 void delete_tempfile(struct tempfile *tempfile)
 229 {
 230         if (!tempfile->active)
 231                 return;
 232
 233         if (!close_tempfile(tempfile)) {
 234                 unlink_or_warn(tempfile->filename.buf);
 235                 tempfile->active = 0;
 236                 strbuf_reset(&tempfile->filename);
 237         }
 238 }