A lot of work went into defining the state diagram for lockfiles and
ensuring correct, race-resistant cleanup in all circumstances.
Most of that infrastructure can be applied directly to *any* temporary
file. So extract a new "tempfile" module from the "lockfile" module.
Reimplement lockfile on top of tempfile.
Subsequent commits will add more users of the new module.
Signed-off-by: Michael Haggerty <mhagger@xxxxxxxxxxxx>
---
Makefile | 1 +
lockfile.c | 261 ++++---------------------------------------------------------
lockfile.h | 73 +++++++++++------
tempfile.c | 238 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
tempfile.h | 167 +++++++++++++++++++++++++++++++++++++++
5 files changed, 470 insertions(+), 270 deletions(-)
create mode 100644 tempfile.c
create mode 100644 tempfile.h
diff --git a/Makefile b/Makefile
index 54ec511..2573f89 100644
--- a/Makefile
+++ b/Makefile
@@ -786,6 +786,7 @@ LIB_OBJS += string-list.o
LIB_OBJS += submodule.o
LIB_OBJS += symlinks.o
LIB_OBJS += tag.o
+LIB_OBJS += tempfile.o
LIB_OBJS += trace.o
LIB_OBJS += trailer.o
LIB_OBJS += transport.o
diff --git a/lockfile.c b/lockfile.c
index 3904803..e1d68f7 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -2,90 +2,8 @@
* Copyright (c) 2005, Junio C Hamano
*/
-/*
- * State diagram and cleanup
- * -------------------------
- *
- * This module keeps track of all locked files in `lock_file_list` for
- * use at cleanup. This list and the `lock_file` objects that comprise
- * it must be kept in self-consistent states at all time, because the
- * program can be interrupted any time by a signal, in which case the
- * signal handler will walk through the list attempting to clean up
- * any open lock files.
- *
- * The possible states of a `lock_file` 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 `lock_file_list`, and `on_list` is set.
- *
- * - Locked, lockfile open (after `hold_lock_file_for_update()`,
- * `hold_lock_file_for_append()`, or `reopen_lock_file()`). In this
- * state:
- *
- * - the lockfile exists
- * - `active` is set
- * - `filename` holds the filename of the lockfile
- * - `fd` holds a file descriptor open for writing to the lockfile
- * - `fp` holds a pointer to an open `FILE` object if and only if
- * `fdopen_lock_file()` has been called on the object
- * - `owner` holds the PID of the process that locked the file
- *
- * - Locked, lockfile closed (after successful `close_lock_file()`).
- * Same as the previous state, except that the lockfile is closed
- * and `fd` is -1.
- *
- * - Unlocked (after `commit_lock_file()`, `commit_lock_file_to()`,
- * `rollback_lock_file()`, a failed attempt to lock, or a failed
- * `close_lock_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
- * - the object is left registered in the `lock_file_list`, and
- * `on_list` is set.
- *
- * A lockfile is owned by the process that created it. The `lock_file`
- * has an `owner` field that records the owner's PID. This field is
- * used to prevent a forked process from closing a lockfile created by
- * its parent.
- */
-
#include "cache.h"
#include "lockfile.h"
-#include "sigchain.h"
-
-static struct lock_file *volatile lock_file_list;
-
-static void remove_lock_files(int skip_fclose)
-{
- pid_t me = getpid();
-
- while (lock_file_list) {
- if (lock_file_list->owner == me) {
- /* fclose() is not safe to call in a signal handler */
- if (skip_fclose)
- lock_file_list->fp = NULL;
- rollback_lock_file(lock_file_list);
- }
- lock_file_list = lock_file_list->next;
- }
-}
-
-static void remove_lock_files_on_exit(void)
-{
- remove_lock_files(0);
-}
-
-static void remove_lock_files_on_signal(int signo)
-{
- remove_lock_files(1);
- sigchain_pop(signo);
- raise(signo);
-}
/*
* path = absolute or relative path name
@@ -154,60 +72,17 @@ static void resolve_symlink(struct strbuf *path)
/* Make sure errno contains a meaningful value on error */
static int lock_file(struct lock_file *lk, const char *path, int flags)
{
- size_t pathlen = strlen(path);
-
- if (!lock_file_list) {
- /* One-time initialization */
- sigchain_push_common(remove_lock_files_on_signal);
- atexit(remove_lock_files_on_exit);
- }
+ int fd;
+ struct strbuf filename = STRBUF_INIT;
- if (lk->active)
- die("BUG: cannot lock_file(\"%s\") using active struct lock_file",
- path);
- if (!lk->on_list) {
- /* Initialize *lk and add it to lock_file_list: */
- lk->fd = -1;
- lk->fp = NULL;
- lk->active = 0;
- lk->owner = 0;
- strbuf_init(&lk->filename, pathlen + LOCK_SUFFIX_LEN);
- lk->next = lock_file_list;
- lock_file_list = lk;
- lk->on_list = 1;
- } else if (lk->filename.len) {
- /* This shouldn't happen, but better safe than sorry. */
- die("BUG: lock_file(\"%s\") called with improperly-reset lock_file object",
- path);
- }
+ strbuf_addstr(&filename, path);
+ if (!(flags & LOCK_NO_DEREF))
+ resolve_symlink(&filename);
- if (flags & LOCK_NO_DEREF) {
- strbuf_add_absolute_path(&lk->filename, path);
- } else {
- struct strbuf resolved_path = STRBUF_INIT;
-
- strbuf_add(&resolved_path, path, pathlen);
- resolve_symlink(&resolved_path);
- strbuf_add_absolute_path(&lk->filename, resolved_path.buf);
- strbuf_release(&resolved_path);
- }
-
- strbuf_addstr(&lk->filename, LOCK_SUFFIX);
- lk->fd = open(lk->filename.buf, O_RDWR | O_CREAT | O_EXCL, 0666);
- if (lk->fd < 0) {
- strbuf_reset(&lk->filename);
- return -1;
- }
- lk->owner = getpid();
- lk->active = 1;
- if (adjust_shared_perm(lk->filename.buf)) {
- int save_errno = errno;
- error("cannot fix permission bits on %s", lk->filename.buf);
- rollback_lock_file(lk);
- errno = save_errno;
- return -1;
- }
- return lk->fd;
+ strbuf_addstr(&filename, LOCK_SUFFIX);
+ fd = create_tempfile(&lk->tempfile, filename.buf);
+ strbuf_release(&filename);
+ return fd;
}
static int sleep_microseconds(long us)
@@ -353,109 +228,17 @@ int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
return fd;
}
-FILE *fdopen_lock_file(struct lock_file *lk, const char *mode)
-{
- if (!lk->active)
- die("BUG: fdopen_lock_file() called for unlocked object");
- if (lk->fp)
- die("BUG: fdopen_lock_file() called twice for file '%s'", lk->filename.buf);
-
- lk->fp = fdopen(lk->fd, mode);
- return lk->fp;
-}
-
-const char *get_lock_file_path(struct lock_file *lk)
-{
- if (!lk->active)
- die("BUG: get_lock_file_path() called for unlocked object");
- return lk->filename.buf;
-}
-
-int get_lock_file_fd(struct lock_file *lk)
-{
- if (!lk->active)
- die("BUG: get_lock_file_fd() called for unlocked object");
- return lk->fd;
-}
-
-FILE *get_lock_file_fp(struct lock_file *lk)
-{
- if (!lk->active)
- die("BUG: get_lock_file_fp() called for unlocked object");
- return lk->fp;
-}
-
char *get_locked_file_path(struct lock_file *lk)
{
- if (!lk->active)
- die("BUG: get_locked_file_path() called for unlocked object");
- if (lk->filename.len <= LOCK_SUFFIX_LEN ||
- strcmp(lk->filename.buf + lk->filename.len - LOCK_SUFFIX_LEN, LOCK_SUFFIX))
+ struct strbuf ret = STRBUF_INIT;
+
+ strbuf_addstr(&ret, get_tempfile_path(&lk->tempfile));
+ if (ret.len <= LOCK_SUFFIX_LEN ||
+ strcmp(ret.buf + ret.len - LOCK_SUFFIX_LEN, LOCK_SUFFIX))
die("BUG: get_locked_file_path() called for malformed lock object");
/* remove ".lock": */
- return xmemdupz(lk->filename.buf, lk->filename.len - LOCK_SUFFIX_LEN);
-}
-
-int close_lock_file(struct lock_file *lk)
-{
- int fd = lk->fd;
- FILE *fp = lk->fp;
- int err;
-
- if (fd < 0)
- return 0;
-
- lk->fd = -1;
- if (fp) {
- lk->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;
- rollback_lock_file(lk);
- errno = save_errno;
- return -1;
- }
-
- return 0;
-}
-
-int reopen_lock_file(struct lock_file *lk)
-{
- if (0 <= lk->fd)
- die(_("BUG: reopen a lockfile that is still open"));
- if (!lk->active)
- die(_("BUG: reopen a lockfile that has been committed"));
- lk->fd = open(lk->filename.buf, O_WRONLY);
- return lk->fd;
-}
-
-int commit_lock_file_to(struct lock_file *lk, const char *path)
-{
- if (!lk->active)
- die("BUG: attempt to commit unlocked object to \"%s\"", path);
-
- if (close_lock_file(lk))
- return -1;
-
- if (rename(lk->filename.buf, path)) {
- int save_errno = errno;
- rollback_lock_file(lk);
- errno = save_errno;
- return -1;
- }
-
- lk->active = 0;
- strbuf_reset(&lk->filename);
- return 0;
+ strbuf_setlen(&ret, ret.len - LOCK_SUFFIX_LEN);
+ return strbuf_detach(&ret, NULL);
}
int commit_lock_file(struct lock_file *lk)
@@ -471,15 +254,3 @@ int commit_lock_file(struct lock_file *lk)
free(result_path);
return 0;
}
-
-void rollback_lock_file(struct lock_file *lk)
-{
- if (!lk->active)
- return;
-
- if (!close_lock_file(lk)) {
- unlink_or_warn(lk->filename.buf);
- lk->active = 0;
- strbuf_reset(&lk->filename);
- }
-}
diff --git a/lockfile.h b/lockfile.h
index a204ab6..8131fa3 100644
--- a/lockfile.h
+++ b/lockfile.h
@@ -29,6 +29,8 @@
* the file or the new contents of the file (assuming that the
* filesystem implements `rename(2)` atomically).
*
+ * Most of the heavy lifting is done by the tempfile module (see
+ * "tempfile.h").
*
* Calling sequence
* ----------------
@@ -74,19 +76,19 @@
* `hold_lock_file_for_update()` or `hold_lock_file_for_append()`.
*
* If the program exits before `commit_lock_file()`,
- * `commit_lock_file_to()`, or `rollback_lock_file()` is called, an
- * `atexit(3)` handler will close and remove the lockfile, thereby
- * rolling back any uncommitted changes.
+ * `commit_lock_file_to()`, or `rollback_lock_file()` is called, the
+ * tempfile module will close and remove the lockfile, thereby rolling
+ * back any uncommitted changes.
*
* If you need to close the file descriptor you obtained from a
* `hold_lock_file_for_*()` function yourself, do so by calling
- * `close_lock_file()`. You should never call `close(2)` or
- * `fclose(3)` yourself, otherwise the `struct lock_file` structure
- * would still think that the file descriptor needs to be closed, and
- * a commit or rollback would result in duplicate calls to `close(2)`.
- * Worse yet, if you close and then later open another file descriptor
- * for a completely different purpose, then a commit or rollback might
- * close that unrelated file descriptor.
+ * `close_lock_file()`. See "tempfile.h" for more information.
+ *
+ *
+ * Under the covers, a lockfile is just a tempfile with a few helper
+ * functions. In particular, the state diagram and the cleanup
+ * machinery are all implemented in the tempfile module.
+ *
*
* Error handling
* --------------
@@ -103,14 +105,10 @@
* -1.
*/
+#include "tempfile.h"
+
struct lock_file {
- struct lock_file *volatile next;
- volatile sig_atomic_t active;
- volatile int fd;
- FILE *volatile fp;
- volatile pid_t owner;
- char on_list;
- struct strbuf filename;
+ struct tempfile tempfile;
};
/* String appended to a filename to derive the lockfile name: */
@@ -201,16 +199,29 @@ extern NORETURN void unable_to_lock_die(const char *path, int err);
* error. The stream is closed automatically when `close_lock_file()`
* is called or when the file is committed or rolled back.
*/
-extern FILE *fdopen_lock_file(struct lock_file *lk, const char *mode);
+static inline FILE *fdopen_lock_file(struct lock_file *lk, const char *mode)
+{
+ return fdopen_tempfile(&lk->tempfile, mode);
+}
/*
* Return the path of the lockfile. The return value is a pointer to a
* field within the lock_file object and should not be freed.
*/
-extern const char *get_lock_file_path(struct lock_file *lk);
+static inline const char *get_lock_file_path(struct lock_file *lk)
+{
+ return get_tempfile_path(&lk->tempfile);
+}
-extern int get_lock_file_fd(struct lock_file *lk);
-extern FILE *get_lock_file_fp(struct lock_file *lk);
+static inline int get_lock_file_fd(struct lock_file *lk)
+{
+ return get_tempfile_fd(&lk->tempfile);
+}
+
+static inline FILE *get_lock_file_fp(struct lock_file *lk)
+{
+ return get_tempfile_fp(&lk->tempfile);
+}
/*
* Return the path of the file that is locked by the specified
@@ -227,7 +238,10 @@ extern char *get_locked_file_path(struct lock_file *lk);
* or `rollback_lock_file()` should eventually be called if
* `close_lock_file()` succeeds.
*/
-extern int close_lock_file(struct lock_file *lk);
+static inline int close_lock_file(struct lock_file *lk)
+{
+ return close_tempfile(&lk->tempfile);
+}
/*
* Re-open a lockfile that has been closed using `close_lock_file()`
@@ -248,7 +262,10 @@ extern int close_lock_file(struct lock_file *lk);
*
* * `commit_lock_file()` to make the final version permanent.
*/
-extern int reopen_lock_file(struct lock_file *lk);
+static inline int reopen_lock_file(struct lock_file *lk)
+{
+ return reopen_tempfile(&lk->tempfile);
+}
/*
* Commit the change represented by `lk`: close the file descriptor
@@ -265,7 +282,10 @@ extern int commit_lock_file(struct lock_file *lk);
* Like `commit_lock_file()`, but rename the lockfile to the provided
* `path`. `path` must be on the same filesystem as the lock file.
*/
-extern int commit_lock_file_to(struct lock_file *lk, const char *path);
+static inline int commit_lock_file_to(struct lock_file *lk, const char *path)
+{
+ return rename_tempfile(&lk->tempfile, path);
+}
/*
* Roll back `lk`: close the file descriptor and/or file pointer and
@@ -273,6 +293,9 @@ extern int commit_lock_file_to(struct lock_file *lk, const char *path);
* for a `lock_file` object that has already been committed or rolled
* back.
*/
-extern void rollback_lock_file(struct lock_file *lk);
+static inline void rollback_lock_file(struct lock_file *lk)
+{
+ delete_tempfile(&lk->tempfile);
+}
#endif /* LOCKFILE_H */
diff --git a/tempfile.c b/tempfile.c
new file mode 100644
index 0000000..d835818
--- /dev/null
+++ b/tempfile.c
@@ -0,0 +1,238 @@
+/*
+ * 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);
+ }
+}
diff --git a/tempfile.h b/tempfile.h
new file mode 100644
index 0000000..bcc229f
--- /dev/null
+++ b/tempfile.h
@@ -0,0 +1,167 @@
+#ifndef TEMPFILE_H
+#define TEMPFILE_H
+
+/*
+ * Handle temporary files.
+ *
+ * The tempfile API allows temporary files to be created, deleted, and
+ * atomically renamed. Temporary files that are still active when the
+ * program ends are cleaned up automatically. Lockfiles (see
+ * "lockfile.h") are built on top of this API.
+ *
+ *
+ * Calling sequence
+ * ----------------
+ *
+ * The caller:
+ *
+ * * Allocates a `struct tempfile` either as a static variable or on
+ * the heap, initialized to zeros. Once you use the structure to
+ * call `create_tempfile()`, it belongs to the tempfile subsystem
+ * and its storage must remain valid throughout the life of the
+ * program (i.e. you cannot use an on-stack variable to hold this
+ * structure).
+ *
+ * * Attempts to create a temporary file by calling
+ * `create_tempfile()`.
+ *
+ * * Writes new content to the file by either:
+ *
+ * * writing to the file descriptor returned by `create_tempfile()`
+ * (also available via `tempfile->fd`).
+ *
+ * * calling `fdopen_tempfile()` to get a `FILE` pointer for the
+ * open file and writing to the file using stdio.
+ *
+ * When finished writing, the caller can:
+ *
+ * * Close the file descriptor and remove the temporary file by
+ * calling `delete_tempfile()`.
+ *
+ * * Close the temporary file and rename it atomically to a specified
+ * filename by calling `rename_tempfile()`. This relinquishes
+ * control of the file.
+ *
+ * * Close the file descriptor without removing or renaming the
+ * temporary file by calling `close_tempfile()`, and later call
+ * `delete_tempfile()` or `rename_tempfile()`.
+ *
+ * Even after the temporary file is renamed or deleted, the `tempfile`
+ * object must not be freed or altered by the caller. However, it may
+ * be reused; just pass it to another call of `create_tempfile()`.
+ *
+ * If the program exits before `rename_tempfile()` or
+ * `delete_tempfile()` is called, an `atexit(3)` handler will close
+ * and remove the temporary file.
+ *
+ * If you need to close the file descriptor yourself, do so by calling
+ * `close_tempfile()`. You should never call `close(2)` or `fclose(3)`
+ * yourself, otherwise the `struct tempfile` structure would still
+ * think that the file descriptor needs to be closed, and a later
+ * cleanup would result in duplicate calls to `close(2)`. Worse yet,
+ * if you close and then later open another file descriptor for a
+ * completely different purpose, then the unrelated file descriptor
+ * might get closed.
+ *
+ *
+ * Error handling
+ * --------------
+ *
+ * `create_tempfile()` returns a file descriptor on success or -1 on
+ * failure. On errors, `errno` describes the reason for failure.
+ *
+ * `delete_tempfile()`, `rename_tempfile()`, and `close_tempfile()`
+ * return 0 on success. On failure they set `errno` appropriately, do
+ * their best to delete the temporary file, and return -1.
+ */
+
+struct tempfile {
+ struct tempfile *volatile next;
+ volatile sig_atomic_t active;
+ volatile int fd;
+ FILE *volatile fp;
+ volatile pid_t owner;
+ char on_list;
+ struct strbuf filename;
+};
+
+/*
+ * Attempt to create a temporary file at the specified `path`. Return
+ * a file descriptor for writing to it, or -1 on error. It is an error
+ * if a file already exists at that path.
+ */
+extern int create_tempfile(struct tempfile *tempfile, const char *path);
+
+/*
+ * Associate a stdio stream with the temporary file (which must still
+ * be open). Return `NULL` (*without* deleting the file) on error. The
+ * stream is closed automatically when `close_tempfile()` is called or
+ * when the file is deleted or renamed.
+ */
+extern FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode);
+
+static inline int is_tempfile_active(struct tempfile *tempfile)
+{
+ return tempfile->active;
+}
+
+/*
+ * Return the path of the lockfile. The return value is a pointer to a
+ * field within the lock_file object and should not be freed.
+ */
+extern const char *get_tempfile_path(struct tempfile *tempfile);
+
+extern int get_tempfile_fd(struct tempfile *tempfile);
+extern FILE *get_tempfile_fp(struct tempfile *tempfile);
+
+/*
+ * If the temporary file is still open, close it (and the file pointer
+ * too, if it has been opened using `fdopen_tempfile()`) without
+ * deleting the file. Return 0 upon success. On failure to `close(2)`,
+ * return a negative value and delete the file. Usually
+ * `delete_tempfile()` or `rename_tempfile()` should eventually be
+ * called if `close_tempfile()` succeeds.
+ */
+extern int close_tempfile(struct tempfile *tempfile);
+
+/*
+ * Re-open a temporary file that has been closed using
+ * `close_tempfile()` but not yet deleted or renamed. This can be used
+ * to implement a sequence of operations like the following:
+ *
+ * * Create temporary file.
+ *
+ * * Write new contents to file, then `close_tempfile()` to cause the
+ * contents to be written to disk.
+ *
+ * * Pass the name of the temporary file to another program to allow
+ * it (and nobody else) to inspect or even modify the file's
+ * contents.
+ *
+ * * `reopen_tempfile()` to reopen the temporary file. Make further
+ * updates to the contents.
+ *
+ * * `rename_tempfile()` to move the file to its permanent location.
+ */
+extern int reopen_tempfile(struct tempfile *tempfile);
+
+/*
+ * Close the file descriptor and/or file pointer and remove the
+ * temporary file associated with `tempfile`. It is a NOOP to call
+ * `delete_tempfile()` for a `tempfile` object that has already been
+ * deleted or renamed.
+ */
+extern void delete_tempfile(struct tempfile *tempfile);
+
+/*
+ * Close the file descriptor and/or file pointer if they are still
+ * open, and atomically rename the temporary file to `path`. `path`
+ * must be on the same filesystem as the lock file. Return 0 on
+ * success. On failure, delete the temporary file and return -1, with
+ * `errno` set to the value from the failing call to `close(2)` or
+ * `rename(2)`. It is a bug to call `rename_tempfile()` for a
+ * `tempfile` object that is not currently active.
+ */
+extern int rename_tempfile(struct tempfile *tempfile, const char *path);
+
+#endif /* TEMPFILE_H */
--
2.5.0
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