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-rw-r--r--tempfile.c238
1 files changed, 238 insertions, 0 deletions
diff --git a/tempfile.c b/tempfile.c
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+/*
+ * State diagram and cleanup
+ * -------------------------
+ *
+ * If the program exits while a temporary file is active, we want to
+ * make sure that we remove it. This is done by remembering the active
+ * temporary files in a linked list, `tempfile_list`. An `atexit(3)`
+ * handler and a signal handler are registered, to clean up any active
+ * temporary files.
+ *
+ * Because the signal handler can run at any time, `tempfile_list` and
+ * the `tempfile` objects that comprise it must be kept in
+ * self-consistent states at all times.
+ *
+ * The possible states of a `tempfile` object are as follows:
+ *
+ * - Uninitialized. In this state the object's `on_list` field must be
+ * zero but the rest of its contents need not be initialized. As
+ * soon as the object is used in any way, it is irrevocably
+ * registered in `tempfile_list`, and `on_list` is set.
+ *
+ * - Active, file open (after `create_tempfile()` or
+ * `reopen_tempfile()`). In this state:
+ *
+ * - the temporary file exists
+ * - `active` is set
+ * - `filename` holds the filename of the temporary file
+ * - `fd` holds a file descriptor open for writing to it
+ * - `fp` holds a pointer to an open `FILE` object if and only if
+ * `fdopen_tempfile()` has been called on the object
+ * - `owner` holds the PID of the process that created the file
+ *
+ * - Active, file closed (after successful `close_tempfile()`). Same
+ * as the previous state, except that the temporary file is closed,
+ * `fd` is -1, and `fp` is `NULL`.
+ *
+ * - Inactive (after `delete_tempfile()`, `rename_tempfile()`, a
+ * failed attempt to create a temporary file, or a failed
+ * `close_tempfile()`). In this state:
+ *
+ * - `active` is unset
+ * - `filename` is empty (usually, though there are transitory
+ * states in which this condition doesn't hold). Client code should
+ * *not* rely on the filename being empty in this state.
+ * - `fd` is -1 and `fp` is `NULL`
+ * - the object is left registered in the `tempfile_list`, and
+ * `on_list` is set.
+ *
+ * A temporary file is owned by the process that created it. The
+ * `tempfile` has an `owner` field that records the owner's PID. This
+ * field is used to prevent a forked process from deleting a temporary
+ * file created by its parent.
+ */
+
+#include "cache.h"
+#include "tempfile.h"
+#include "sigchain.h"
+
+static struct tempfile *volatile tempfile_list;
+
+static void remove_tempfiles(int skip_fclose)
+{
+ pid_t me = getpid();
+
+ while (tempfile_list) {
+ if (tempfile_list->owner == me) {
+ /* fclose() is not safe to call in a signal handler */
+ if (skip_fclose)
+ tempfile_list->fp = NULL;
+ delete_tempfile(tempfile_list);
+ }
+ tempfile_list = tempfile_list->next;
+ }
+}
+
+static void remove_tempfiles_on_exit(void)
+{
+ remove_tempfiles(0);
+}
+
+static void remove_tempfiles_on_signal(int signo)
+{
+ remove_tempfiles(1);
+ sigchain_pop(signo);
+ raise(signo);
+}
+
+/* Make sure errno contains a meaningful value on error */
+int create_tempfile(struct tempfile *tempfile, const char *path)
+{
+ size_t pathlen = strlen(path);
+
+ if (!tempfile_list) {
+ /* One-time initialization */
+ sigchain_push_common(remove_tempfiles_on_signal);
+ atexit(remove_tempfiles_on_exit);
+ }
+
+ if (tempfile->active)
+ die("BUG: create_tempfile called for active object");
+ if (!tempfile->on_list) {
+ /* Initialize *tempfile and add it to tempfile_list: */
+ tempfile->fd = -1;
+ tempfile->fp = NULL;
+ tempfile->active = 0;
+ tempfile->owner = 0;
+ strbuf_init(&tempfile->filename, pathlen);
+ tempfile->next = tempfile_list;
+ tempfile_list = tempfile;
+ tempfile->on_list = 1;
+ } else if (tempfile->filename.len) {
+ /* This shouldn't happen, but better safe than sorry. */
+ die("BUG: create_tempfile called for improperly-reset object");
+ }
+
+ strbuf_add_absolute_path(&tempfile->filename, path);
+ tempfile->fd = open(tempfile->filename.buf, O_RDWR | O_CREAT | O_EXCL, 0666);
+ if (tempfile->fd < 0) {
+ strbuf_reset(&tempfile->filename);
+ return -1;
+ }
+ tempfile->owner = getpid();
+ tempfile->active = 1;
+ if (adjust_shared_perm(tempfile->filename.buf)) {
+ int save_errno = errno;
+ error("cannot fix permission bits on %s", tempfile->filename.buf);
+ delete_tempfile(tempfile);
+ errno = save_errno;
+ return -1;
+ }
+ return tempfile->fd;
+}
+
+FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode)
+{
+ if (!tempfile->active)
+ die("BUG: fdopen_tempfile() called for inactive object");
+ if (tempfile->fp)
+ die("BUG: fdopen_tempfile() called for open object");
+
+ tempfile->fp = fdopen(tempfile->fd, mode);
+ return tempfile->fp;
+}
+
+const char *get_tempfile_path(struct tempfile *tempfile)
+{
+ if (!tempfile->active)
+ die("BUG: get_tempfile_path() called for inactive object");
+ return tempfile->filename.buf;
+}
+
+int get_tempfile_fd(struct tempfile *tempfile)
+{
+ if (!tempfile->active)
+ die("BUG: get_tempfile_fd() called for inactive object");
+ return tempfile->fd;
+}
+
+FILE *get_tempfile_fp(struct tempfile *tempfile)
+{
+ if (!tempfile->active)
+ die("BUG: get_tempfile_fp() called for inactive object");
+ return tempfile->fp;
+}
+
+int close_tempfile(struct tempfile *tempfile)
+{
+ int fd = tempfile->fd;
+ FILE *fp = tempfile->fp;
+ int err;
+
+ if (fd < 0)
+ return 0;
+
+ tempfile->fd = -1;
+ if (fp) {
+ tempfile->fp = NULL;
+
+ /*
+ * Note: no short-circuiting here; we want to fclose()
+ * in any case!
+ */
+ err = ferror(fp) | fclose(fp);
+ } else {
+ err = close(fd);
+ }
+
+ if (err) {
+ int save_errno = errno;
+ delete_tempfile(tempfile);
+ errno = save_errno;
+ return -1;
+ }
+
+ return 0;
+}
+
+int reopen_tempfile(struct tempfile *tempfile)
+{
+ if (0 <= tempfile->fd)
+ die("BUG: reopen_tempfile called for an open object");
+ if (!tempfile->active)
+ die("BUG: reopen_tempfile called for an inactive object");
+ tempfile->fd = open(tempfile->filename.buf, O_WRONLY);
+ return tempfile->fd;
+}
+
+int rename_tempfile(struct tempfile *tempfile, const char *path)
+{
+ if (!tempfile->active)
+ die("BUG: rename_tempfile called for inactive object");
+
+ if (close_tempfile(tempfile))
+ return -1;
+
+ if (rename(tempfile->filename.buf, path)) {
+ int save_errno = errno;
+ delete_tempfile(tempfile);
+ errno = save_errno;
+ return -1;
+ }
+
+ tempfile->active = 0;
+ strbuf_reset(&tempfile->filename);
+ return 0;
+}
+
+void delete_tempfile(struct tempfile *tempfile)
+{
+ if (!tempfile->active)
+ return;
+
+ if (!close_tempfile(tempfile)) {
+ unlink_or_warn(tempfile->filename.buf);
+ tempfile->active = 0;
+ strbuf_reset(&tempfile->filename);
+ }
+}