1 files changed, 321 insertions, 0 deletions
diff --git a/tempfile.c b/tempfile.c
new file mode 100644
index 0000000000..5fdafdd2d2
--- /dev/null
+++ b/tempfile.c
@@ -0,0 +1,321 @@
+/*
+ * 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 `close_tempfile_gently()`). 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()`, or a
+ *   failed attempt to create a temporary file). 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 removed from `tempfile_list` (but could be used again)
+ *
+ * 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 VOLATILE_LIST_HEAD(tempfile_list);
+
+static void remove_tempfiles(int in_signal_handler)
+{
+	pid_t me = getpid();
+	volatile struct volatile_list_head *pos;
+
+	list_for_each(pos, &tempfile_list) {
+		struct tempfile *p = list_entry(pos, struct tempfile, list);
+
+		if (!is_tempfile_active(p) || p->owner != me)
+			continue;
+
+		if (p->fd >= 0)
+			close(p->fd);
+
+		if (in_signal_handler)
+			unlink(p->filename.buf);
+		else
+			unlink_or_warn(p->filename.buf);
+
+		p->active = 0;
+	}
+}
+
+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);
+}
+
+static struct tempfile *new_tempfile(void)
+{
+	struct tempfile *tempfile = xmalloc(sizeof(*tempfile));
+	tempfile->fd = -1;
+	tempfile->fp = NULL;
+	tempfile->active = 0;
+	tempfile->owner = 0;
+	INIT_LIST_HEAD(&tempfile->list);
+	strbuf_init(&tempfile->filename, 0);
+	return tempfile;
+}
+
+static void activate_tempfile(struct tempfile *tempfile)
+{
+	static int initialized;
+
+	if (is_tempfile_active(tempfile))
+		BUG("activate_tempfile called for active object");
+
+	if (!initialized) {
+		sigchain_push_common(remove_tempfiles_on_signal);
+		atexit(remove_tempfiles_on_exit);
+		initialized = 1;
+	}
+
+	volatile_list_add(&tempfile->list, &tempfile_list);
+	tempfile->owner = getpid();
+	tempfile->active = 1;
+}
+
+static void deactivate_tempfile(struct tempfile *tempfile)
+{
+	tempfile->active = 0;
+	strbuf_release(&tempfile->filename);
+	volatile_list_del(&tempfile->list);
+	free(tempfile);
+}
+
+/* Make sure errno contains a meaningful value on error */
+struct tempfile *create_tempfile(const char *path)
+{
+	struct tempfile *tempfile = new_tempfile();
+
+	strbuf_add_absolute_path(&tempfile->filename, path);
+	tempfile->fd = open(tempfile->filename.buf,
+			    O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, 0666);
+	if (O_CLOEXEC && tempfile->fd < 0 && errno == EINVAL)
+		/* Try again w/o O_CLOEXEC: the kernel might not support it */
+		tempfile->fd = open(tempfile->filename.buf,
+				    O_RDWR | O_CREAT | O_EXCL, 0666);
+	if (tempfile->fd < 0) {
+		deactivate_tempfile(tempfile);
+		return NULL;
+	}
+	activate_tempfile(tempfile);
+	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 NULL;
+	}
+
+	return tempfile;
+}
+
+struct tempfile *register_tempfile(const char *path)
+{
+	struct tempfile *tempfile = new_tempfile();
+	strbuf_add_absolute_path(&tempfile->filename, path);
+	activate_tempfile(tempfile);
+	return tempfile;
+}
+
+struct tempfile *mks_tempfile_sm(const char *template, int suffixlen, int mode)
+{
+	struct tempfile *tempfile = new_tempfile();
+
+	strbuf_add_absolute_path(&tempfile->filename, template);
+	tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
+	if (tempfile->fd < 0) {
+		deactivate_tempfile(tempfile);
+		return NULL;
+	}
+	activate_tempfile(tempfile);
+	return tempfile;
+}
+
+struct tempfile *mks_tempfile_tsm(const char *template, int suffixlen, int mode)
+{
+	struct tempfile *tempfile = new_tempfile();
+	const char *tmpdir;
+
+	tmpdir = getenv("TMPDIR");
+	if (!tmpdir)
+		tmpdir = "/tmp";
+
+	strbuf_addf(&tempfile->filename, "%s/%s", tmpdir, template);
+	tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
+	if (tempfile->fd < 0) {
+		deactivate_tempfile(tempfile);
+		return NULL;
+	}
+	activate_tempfile(tempfile);
+	return tempfile;
+}
+
+struct tempfile *xmks_tempfile_m(const char *template, int mode)
+{
+	struct tempfile *tempfile;
+	struct strbuf full_template = STRBUF_INIT;
+
+	strbuf_add_absolute_path(&full_template, template);
+	tempfile = mks_tempfile_m(full_template.buf, mode);
+	if (!tempfile)
+		die_errno("Unable to create temporary file '%s'",
+			  full_template.buf);
+
+	strbuf_release(&full_template);
+	return tempfile;
+}
+
+FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode)
+{
+	if (!is_tempfile_active(tempfile))
+		BUG("fdopen_tempfile() called for inactive object");
+	if (tempfile->fp)
+		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 (!is_tempfile_active(tempfile))
+		BUG("get_tempfile_path() called for inactive object");
+	return tempfile->filename.buf;
+}
+
+int get_tempfile_fd(struct tempfile *tempfile)
+{
+	if (!is_tempfile_active(tempfile))
+		BUG("get_tempfile_fd() called for inactive object");
+	return tempfile->fd;
+}
+
+FILE *get_tempfile_fp(struct tempfile *tempfile)
+{
+	if (!is_tempfile_active(tempfile))
+		BUG("get_tempfile_fp() called for inactive object");
+	return tempfile->fp;
+}
+
+int close_tempfile_gently(struct tempfile *tempfile)
+{
+	int fd;
+	FILE *fp;
+	int err;
+
+	if (!is_tempfile_active(tempfile) || tempfile->fd < 0)
+		return 0;
+
+	fd = tempfile->fd;
+	fp = tempfile->fp;
+	tempfile->fd = -1;
+	if (fp) {
+		tempfile->fp = NULL;
+		if (ferror(fp)) {
+			err = -1;
+			if (!fclose(fp))
+				errno = EIO;
+		} else {
+			err = fclose(fp);
+		}
+	} else {
+		err = close(fd);
+	}
+
+	return err ? -1 : 0;
+}
+
+int reopen_tempfile(struct tempfile *tempfile)
+{
+	if (!is_tempfile_active(tempfile))
+		BUG("reopen_tempfile called for an inactive object");
+	if (0 <= tempfile->fd)
+		BUG("reopen_tempfile called for an open object");
+	tempfile->fd = open(tempfile->filename.buf, O_WRONLY);
+	return tempfile->fd;
+}
+
+int rename_tempfile(struct tempfile **tempfile_p, const char *path)
+{
+	struct tempfile *tempfile = *tempfile_p;
+
+	if (!is_tempfile_active(tempfile))
+		BUG("rename_tempfile called for inactive object");
+
+	if (close_tempfile_gently(tempfile)) {
+		delete_tempfile(tempfile_p);
+		return -1;
+	}
+
+	if (rename(tempfile->filename.buf, path)) {
+		int save_errno = errno;
+		delete_tempfile(tempfile_p);
+		errno = save_errno;
+		return -1;
+	}
+
+	deactivate_tempfile(tempfile);
+	*tempfile_p = NULL;
+	return 0;
+}
+
+void delete_tempfile(struct tempfile **tempfile_p)
+{
+	struct tempfile *tempfile = *tempfile_p;
+
+	if (!is_tempfile_active(tempfile))
+		return;
+
+	close_tempfile_gently(tempfile);
+	unlink_or_warn(tempfile->filename.buf);
+	deactivate_tempfile(tempfile);
+	*tempfile_p = NULL;
+}