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Merge branch 'mh/lockfile' 

The lockfile API and its users have been cleaned up.

* mh/lockfile: (38 commits)
  lockfile.h: extract new header file for the functions in lockfile.c
  hold_locked_index(): move from lockfile.c to read-cache.c
  hold_lock_file_for_append(): restore errno before returning
  get_locked_file_path(): new function
  lockfile.c: rename static functions
  lockfile: rename LOCK_NODEREF to LOCK_NO_DEREF
  commit_lock_file_to(): refactor a helper out of commit_lock_file()
  trim_last_path_component(): replace last_path_elm()
  resolve_symlink(): take a strbuf parameter
  resolve_symlink(): use a strbuf for internal scratch space
  lockfile: change lock_file::filename into a strbuf
  commit_lock_file(): use a strbuf to manage temporary space
  try_merge_strategy(): use a statically-allocated lock_file object
  try_merge_strategy(): remove redundant lock_file allocation
  struct lock_file: declare some fields volatile
  lockfile: avoid transitory invalid states
  git_config_set_multivar_in_file(): avoid call to rollback_lock_file()
  dump_marks(): remove a redundant call to rollback_lock_file()
  api-lockfile: document edge cases
  commit_lock_file(): rollback lock file on failure to rename
  ...
maint
Junio C Hamano 2014-10-14 10:49:45 -07:00
parent 7543dea8b2 697cc8efd9
commit bd107e1052
36 changed files with 510 additions and 260 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

234
Documentation/technical/api-lockfile.txt
View File

@ -3,20 +3,128 @@ lockfile API

The lockfile API serves two purposes:

* Mutual exclusion. When we write out a new index file, first
we create a new file `$GIT_DIR/index.lock`, write the new
contents into it, and rename it to the final destination
`$GIT_DIR/index`. We try to create the `$GIT_DIR/index.lock`
file with O_EXCL so that we can notice and fail when somebody
else is already trying to update the index file.
* Mutual exclusion and atomic file updates. When we want to change a
file, we create a lockfile `<filename>.lock`, write the new file
contents into it, and then rename the lockfile to its final
destination `<filename>`. We create the `<filename>.lock` file with
`O_CREAT|O_EXCL` so that we can notice and fail if somebody else has
already locked the file, then atomically rename the lockfile to its
final destination to commit the changes and unlock the file.

* Automatic cruft removal. After we create the "lock" file, we
may decide to `die()`, and we would want to make sure that we
remove the file that has not been committed to its final
destination. This is done by remembering the lockfiles we
created in a linked list and cleaning them up from an
`atexit(3)` handler. Outstanding lockfiles are also removed
when the program dies on a signal.
* Automatic cruft removal. If the program exits after we lock a file
but before the changes have been committed, we want to make sure
that we remove the lockfile. This is done by remembering the
lockfiles we have created in a linked list and setting up an
`atexit(3)` handler and a signal handler that clean up the
lockfiles. This mechanism ensures that outstanding lockfiles are
cleaned up if the program exits (including when `die()` is called)
or if the program dies on a signal.

Please note that lockfiles only block other writers. Readers do not
block, but they are guaranteed to see either the old contents of the
file or the new contents of the file (assuming that the filesystem
implements `rename(2)` atomically).


Calling sequence
----------------

The caller:

* Allocates a `struct lock_file` either as a static variable or on the
heap, initialized to zeros. Once you use the structure to call the
`hold_lock_file_*` family of functions, it belongs to the lockfile
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 lockfile by passing that variable and the path
of the final destination (e.g. `$GIT_DIR/index`) to
`hold_lock_file_for_update` or `hold_lock_file_for_append`.

* Writes new content for the destination file by writing to the file
descriptor returned by those functions (also available via
`lock->fd`).

When finished writing, the caller can:

* Close the file descriptor and rename the lockfile to its final
destination by calling `commit_lock_file` or `commit_lock_file_to`.

* Close the file descriptor and remove the lockfile by calling
`rollback_lock_file`.

* Close the file descriptor without removing or renaming the lockfile
by calling `close_lock_file`, and later call `commit_lock_file`,
`commit_lock_file_to`, `rollback_lock_file`, or `reopen_lock_file`.

Even after the lockfile is committed or rolled back, the `lock_file`
object must not be freed or altered by the caller. However, it may be
reused; just pass it to another call of `hold_lock_file_for_update` or
`hold_lock_file_for_append`.

If the program exits before you have called one of `commit_lock_file`,
`commit_lock_file_to`, `rollback_lock_file`, or `close_lock_file`, an
`atexit(3)` handler will close and remove the lockfile, rolling back
any uncommitted changes.

If you need to close the file descriptor you obtained from a
`hold_lock_file_*` function yourself, do so by calling
`close_lock_file`. You should never call `close(2)` 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(2)`
and then later open another file descriptor for a completely different
purpose, then a commit or rollback might close that unrelated file
descriptor.


Error handling
--------------

The `hold_lock_file_*` functions return a file descriptor on success
or -1 on failure (unless `LOCK_DIE_ON_ERROR` is used; see below). On
errors, `errno` describes the reason for failure. Errors can be
reported by passing `errno` to one of the following helper functions:

unable_to_lock_message::

Append an appropriate error message to a `strbuf`.

unable_to_lock_error::

Emit an appropriate error message using `error()`.

unable_to_lock_die::

Emit an appropriate error message and `die()`.

Similarly, `commit_lock_file`, `commit_lock_file_to`, and
`close_lock_file` return 0 on success. On failure they set `errno`
appropriately, do their best to roll back the lockfile, and return -1.


Flags
-----

The following flags can be passed to `hold_lock_file_for_update` or
`hold_lock_file_for_append`:

LOCK_NO_DEREF::

Usually symbolic links in the destination path are resolved
and the lockfile is created by adding ".lock" to the resolved
path. If `LOCK_NO_DEREF` is set, then the lockfile is created
by adding ".lock" to the path argument itself. This option is
used, for example, when locking a symbolic reference, which
for backwards-compatibility reasons can be a symbolic link
containing the name of the referred-to-reference.

LOCK_DIE_ON_ERROR::

If a lock is already taken for the file, `die()` with an error
message. If this option is not specified, trying to lock a
file that is already locked returns -1 to the caller.


The functions
@ -24,51 +132,77 @@ The functions

hold_lock_file_for_update::

Take a pointer to `struct lock_file`, the filename of
the final destination (e.g. `$GIT_DIR/index`) and a flag
`die_on_error`. Attempt to create a lockfile for the
destination and return the file descriptor for writing
to the file. If `die_on_error` flag is true, it dies if
a lock is already taken for the file; otherwise it
returns a negative integer to the caller on failure.
Take a pointer to `struct lock_file`, the path of the file to
be locked (e.g. `$GIT_DIR/index`) and a flags argument (see
above). Attempt to create a lockfile for the destination and
return the file descriptor for writing to the file.

hold_lock_file_for_append::

Like `hold_lock_file_for_update`, but before returning copy
the existing contents of the file (if any) to the lockfile and
position its write pointer at the end of the file.

get_locked_file_path::

Return the path of the file that is locked by the specified
lock_file object. The caller must free the memory.

commit_lock_file::

Take a pointer to the `struct lock_file` initialized
with an earlier call to `hold_lock_file_for_update()`,
close the file descriptor and rename the lockfile to its
final destination. Returns 0 upon success, a negative
value on failure to close(2) or rename(2).
Take a pointer to the `struct lock_file` initialized with an
earlier call to `hold_lock_file_for_update` or
`hold_lock_file_for_append`, close the file descriptor, and
rename the lockfile to its final destination. Return 0 upon
success. On failure, roll back the lock 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
`commit_lock_file` for a `lock_file` object that is not
currently locked.

commit_lock_file_to::

Like `commit_lock_file()`, except that it takes an explicit
`path` argument to which the lockfile should be renamed. The
`path` must be on the same filesystem as the lock file.

rollback_lock_file::

Take a pointer to the `struct lock_file` initialized
with an earlier call to `hold_lock_file_for_update()`,
close the file descriptor and remove the lockfile.
Take a pointer to the `struct lock_file` initialized with an
earlier call to `hold_lock_file_for_update` or
`hold_lock_file_for_append`, close the file descriptor and
remove the lockfile. It is a NOOP to call
`rollback_lock_file()` for a `lock_file` object that has
already been committed or rolled back.

close_lock_file::
Take a pointer to the `struct lock_file` initialized
with an earlier call to `hold_lock_file_for_update()`,
and close the file descriptor. Returns 0 upon success,
a negative value on failure to close(2).

Because the structure is used in an `atexit(3)` handler, its
storage has to stay throughout the life of the program. It
cannot be an auto variable allocated on the stack.
Take a pointer to the `struct lock_file` initialized with an
earlier call to `hold_lock_file_for_update` or
`hold_lock_file_for_append`, and close the file descriptor.
Return 0 upon success. On failure to `close(2)`, return a
negative value and roll back the lock file. Usually
`commit_lock_file`, `commit_lock_file_to`, or
`rollback_lock_file` should eventually be called if
`close_lock_file` succeeds.

Call `commit_lock_file()` or `rollback_lock_file()` when you are
done writing to the file descriptor. If you do not call either
and simply `exit(3)` from the program, an `atexit(3)` handler
will close and remove the lockfile.
reopen_lock_file::

If you need to close the file descriptor you obtained from
`hold_lock_file_for_update` function yourself, do so by calling
`close_lock_file()`. You should never call `close(2)` yourself!
Otherwise the `struct
lock_file` structure still remembers that the file descriptor
needs to be closed, and a later call to `commit_lock_file()` or
`rollback_lock_file()` will result in duplicate calls to
`close(2)`. Worse yet, if you `close(2)`, open another file
descriptor for completely different purpose, and then call
`commit_lock_file()` or `rollback_lock_file()`, they may close
that unrelated file descriptor.
Re-open a lockfile that has been closed (using
`close_lock_file`) but not yet committed or rolled back. This
can be used to implement a sequence of operations like the
following:

* Lock file.

* Write new contents to lockfile, then `close_lock_file` to
cause the contents to be written to disk.

* Pass the name of the lockfile to another program to allow it
(and nobody else) to inspect the contents you wrote, while
still holding the lock yourself.

* `reopen_lock_file` to reopen the lockfile. Make further
updates to the contents.

* `commit_lock_file` to make the final version permanent.

1
builtin/add.c
View File

@ -5,6 +5,7 @@
*/
#include "cache.h"
#include "builtin.h"
#include "lockfile.h"
#include "dir.h"
#include "pathspec.h"
#include "exec_cmd.h"

1
builtin/apply.c
View File

@ -7,6 +7,7 @@
*
*/
#include "cache.h"
#include "lockfile.h"
#include "cache-tree.h"
#include "quote.h"
#include "blob.h"

2
builtin/checkout-index.c
View File

@ -5,7 +5,7 @@
*
*/
#include "builtin.h"
#include "cache.h"
#include "lockfile.h"
#include "quote.h"
#include "cache-tree.h"
#include "parse-options.h"

2
builtin/checkout.c
View File

@ -1,5 +1,5 @@
#include "cache.h"
#include "builtin.h"
#include "lockfile.h"
#include "parse-options.h"
#include "refs.h"
#include "commit.h"

1
builtin/clone.c
View File

@ -9,6 +9,7 @@
*/

#include "builtin.h"
#include "lockfile.h"
#include "parse-options.h"
#include "fetch-pack.h"
#include "refs.h"

17
builtin/commit.c
View File

@ -6,6 +6,7 @@
*/

#include "cache.h"
#include "lockfile.h"
#include "cache-tree.h"
#include "color.h"
#include "dir.h"
@ -315,8 +316,8 @@ static void refresh_cache_or_die(int refresh_flags)
die_resolve_conflict("commit");
}

static char *prepare_index(int argc, const char **argv, const char *prefix,
const struct commit *current_head, int is_status)
static const char *prepare_index(int argc, const char **argv, const char *prefix,
const struct commit *current_head, int is_status)
{
struct string_list partial;
struct pathspec pathspec;
@ -341,7 +342,7 @@ static char *prepare_index(int argc, const char **argv, const char *prefix,
die(_("unable to create temporary index"));

old_index_env = getenv(INDEX_ENVIRONMENT);
setenv(INDEX_ENVIRONMENT, index_lock.filename, 1);
setenv(INDEX_ENVIRONMENT, index_lock.filename.buf, 1);

if (interactive_add(argc, argv, prefix, patch_interactive) != 0)
die(_("interactive add failed"));
@ -352,7 +353,7 @@ static char *prepare_index(int argc, const char **argv, const char *prefix,
unsetenv(INDEX_ENVIRONMENT);

discard_cache();
read_cache_from(index_lock.filename);
read_cache_from(index_lock.filename.buf);
if (update_main_cache_tree(WRITE_TREE_SILENT) == 0) {
if (reopen_lock_file(&index_lock) < 0)
die(_("unable to write index file"));
@ -362,7 +363,7 @@ static char *prepare_index(int argc, const char **argv, const char *prefix,
warning(_("Failed to update main cache tree"));

commit_style = COMMIT_NORMAL;
return index_lock.filename;
return index_lock.filename.buf;
}

/*
@ -385,7 +386,7 @@ static char *prepare_index(int argc, const char **argv, const char *prefix,
if (write_locked_index(&the_index, &index_lock, CLOSE_LOCK))
die(_("unable to write new_index file"));
commit_style = COMMIT_NORMAL;
return index_lock.filename;
return index_lock.filename.buf;
}

/*
@ -472,9 +473,9 @@ static char *prepare_index(int argc, const char **argv, const char *prefix,
die(_("unable to write temporary index file"));

discard_cache();
read_cache_from(false_lock.filename);
read_cache_from(false_lock.filename.buf);

return false_lock.filename;
return false_lock.filename.buf;
}

static int run_status(FILE *fp, const char *index_file, const char *prefix, int nowarn,

1
builtin/describe.c
View File

@ -1,4 +1,5 @@
#include "cache.h"
#include "lockfile.h"
#include "commit.h"
#include "tag.h"
#include "refs.h"

1
builtin/diff.c
View File

@ -4,6 +4,7 @@
* Copyright (c) 2006 Junio C Hamano
*/
#include "cache.h"
#include "lockfile.h"
#include "color.h"
#include "commit.h"
#include "blob.h"

2
builtin/gc.c
View File

@ -11,7 +11,7 @@
*/

#include "builtin.h"
#include "cache.h"
#include "lockfile.h"
#include "parse-options.h"
#include "run-command.h"
#include "sigchain.h"

16
builtin/merge.c
View File

@ -9,6 +9,7 @@
#include "cache.h"
#include "parse-options.h"
#include "builtin.h"
#include "lockfile.h"
#include "run-command.h"
#include "diff.h"
#include "refs.h"
@ -656,19 +657,18 @@ static int try_merge_strategy(const char *strategy, struct commit_list *common,
struct commit_list *remoteheads,
struct commit *head, const char *head_arg)
{
struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
static struct lock_file lock;

hold_locked_index(lock, 1);
hold_locked_index(&lock, 1);
refresh_cache(REFRESH_QUIET);
if (active_cache_changed &&
write_locked_index(&the_index, lock, COMMIT_LOCK))
write_locked_index(&the_index, &lock, COMMIT_LOCK))
return error(_("Unable to write index."));
rollback_lock_file(lock);
rollback_lock_file(&lock);

if (!strcmp(strategy, "recursive") || !strcmp(strategy, "subtree")) {
int clean, x;
struct commit *result;
struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
struct commit_list *reversed = NULL;
struct merge_options o;
struct commit_list *j;
@ -696,13 +696,13 @@ static int try_merge_strategy(const char *strategy, struct commit_list *common,
for (j = common; j; j = j->next)
commit_list_insert(j->item, &reversed);

hold_locked_index(lock, 1);
hold_locked_index(&lock, 1);
clean = merge_recursive(&o, head,
remoteheads->item, reversed, &result);
if (active_cache_changed &&
write_locked_index(&the_index, lock, COMMIT_LOCK))
write_locked_index(&the_index, &lock, COMMIT_LOCK))
die (_("unable to write %s"), get_index_file());
rollback_lock_file(lock);
rollback_lock_file(&lock);
return clean ? 0 : 1;
} else {
return try_merge_command(strategy, xopts_nr, xopts,

2
builtin/mv.c
View File

@ -3,8 +3,8 @@
*
* Copyright (C) 2006 Johannes Schindelin
*/
#include "cache.h"
#include "builtin.h"
#include "lockfile.h"
#include "dir.h"
#include "cache-tree.h"
#include "string-list.h"

1
builtin/read-tree.c
View File

@ -5,6 +5,7 @@
*/

#include "cache.h"
#include "lockfile.h"
#include "object.h"
#include "tree.h"
#include "tree-walk.h"

1
builtin/receive-pack.c
View File

@ -1,4 +1,5 @@
#include "builtin.h"
#include "lockfile.h"
#include "pack.h"
#include "refs.h"
#include "pkt-line.h"

4
builtin/reflog.c
View File

@ -1,5 +1,5 @@
#include "cache.h"
#include "builtin.h"
#include "lockfile.h"
#include "commit.h"
#include "refs.h"
#include "dir.h"
@ -431,7 +431,7 @@ static int expire_reflog(const char *ref, const unsigned char *sha1, int unused,
write_str_in_full(lock->lock_fd, "\n") != 1 ||
close_ref(lock) < 0)) {
status |= error("Couldn't write %s",
lock->lk->filename);
lock->lk->filename.buf);
unlink(newlog_path);
} else if (rename(newlog_path, log_file)) {
status |= error("cannot rename %s to %s",

1
builtin/reset.c
View File

@ -8,6 +8,7 @@
* Copyright (c) 2005, 2006 Linus Torvalds and Junio C Hamano
*/
#include "builtin.h"
#include "lockfile.h"
#include "tag.h"
#include "object.h"
#include "commit.h"

2
builtin/rm.c
View File

@ -3,8 +3,8 @@
*
* Copyright (C) Linus Torvalds 2006
*/
#include "cache.h"
#include "builtin.h"
#include "lockfile.h"
#include "dir.h"
#include "cache-tree.h"
#include "tree-walk.h"

3
builtin/update-index.c
View File

@ -4,6 +4,7 @@
* Copyright (C) Linus Torvalds, 2005
*/
#include "cache.h"
#include "lockfile.h"
#include "quote.h"
#include "cache-tree.h"
#include "tree-walk.h"
@ -942,7 +943,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
if (newfd < 0) {
if (refresh_args.flags & REFRESH_QUIET)
exit(128);
unable_to_lock_index_die(get_index_file(), lock_error);
unable_to_lock_die(get_index_file(), lock_error);
}
if (write_locked_index(&the_index, lock_file, COMMIT_LOCK))
die("Unable to write new index file");

1
bundle.c
View File

@ -1,4 +1,5 @@
#include "cache.h"
#include "lockfile.h"
#include "bundle.h"
#include "object.h"
#include "commit.h"

1
cache-tree.c
View File

@ -1,4 +1,5 @@
#include "cache.h"
#include "lockfile.h"
#include "tree.h"
#include "tree-walk.h"
#include "cache-tree.h"

20
cache.h
View File

@ -570,29 +570,11 @@ extern void fill_stat_cache_info(struct cache_entry *ce, struct stat *st);
#define REFRESH_IN_PORCELAIN 0x0020 /* user friendly output, not "needs update" */
extern int refresh_index(struct index_state *, unsigned int flags, const struct pathspec *pathspec, char *seen, const char *header_msg);

struct lock_file {
struct lock_file *next;
int fd;
pid_t owner;
char on_list;
char filename[PATH_MAX];
};
#define LOCK_DIE_ON_ERROR 1
#define LOCK_NODEREF 2
extern int unable_to_lock_error(const char *path, int err);
extern void unable_to_lock_message(const char *path, int err,
struct strbuf *buf);
extern NORETURN void unable_to_lock_index_die(const char *path, int err);
extern int hold_lock_file_for_update(struct lock_file *, const char *path, int);
extern int hold_lock_file_for_append(struct lock_file *, const char *path, int);
extern int commit_lock_file(struct lock_file *);
extern int reopen_lock_file(struct lock_file *);
extern void update_index_if_able(struct index_state *, struct lock_file *);

extern int hold_locked_index(struct lock_file *, int);
extern void set_alternate_index_output(const char *);
extern int close_lock_file(struct lock_file *);
extern void rollback_lock_file(struct lock_file *);

extern int delete_ref(const char *, const unsigned char *sha1, int delopt);

/* Environment bits from configuration mechanism */

16
config.c
View File

@ -6,6 +6,7 @@
*
*/
#include "cache.h"
#include "lockfile.h"
#include "exec_cmd.h"
#include "strbuf.h"
#include "quote.h"
@ -2040,9 +2041,9 @@ int git_config_set_multivar_in_file(const char *config_filename,
MAP_PRIVATE, in_fd, 0);
close(in_fd);

if (chmod(lock->filename, st.st_mode & 07777) < 0) {
if (chmod(lock->filename.buf, st.st_mode & 07777) < 0) {
error("chmod on %s failed: %s",
lock->filename, strerror(errno));
lock->filename.buf, strerror(errno));
ret = CONFIG_NO_WRITE;
goto out_free;
}
@ -2099,6 +2100,7 @@ int git_config_set_multivar_in_file(const char *config_filename,
if (commit_lock_file(lock) < 0) {
error("could not commit config file %s", config_filename);
ret = CONFIG_NO_WRITE;
lock = NULL;
goto out_free;
}

@ -2121,7 +2123,7 @@ out_free:
return ret;

write_err_out:
ret = write_error(lock->filename);
ret = write_error(lock->filename.buf);
goto out_free;

}
@ -2222,9 +2224,9 @@ int git_config_rename_section_in_file(const char *config_filename,

fstat(fileno(config_file), &st);

if (chmod(lock->filename, st.st_mode & 07777) < 0) {
if (chmod(lock->filename.buf, st.st_mode & 07777) < 0) {
ret = error("chmod on %s failed: %s",
lock->filename, strerror(errno));
lock->filename.buf, strerror(errno));
goto out;
}

@ -2245,7 +2247,7 @@ int git_config_rename_section_in_file(const char *config_filename,
}
store.baselen = strlen(new_name);
if (!store_write_section(out_fd, new_name)) {
ret = write_error(lock->filename);
ret = write_error(lock->filename.buf);
goto out;
}
/*
@ -2271,7 +2273,7 @@ int git_config_rename_section_in_file(const char *config_filename,
continue;
length = strlen(output);
if (write_in_full(out_fd, output, length) != length) {
ret = write_error(lock->filename);
ret = write_error(lock->filename.buf);
goto out;
}
}

1
credential-store.c
View File

@ -1,4 +1,5 @@
#include "cache.h"
#include "lockfile.h"
#include "credential.h"
#include "string-list.h"
#include "parse-options.h"

5
fast-import.c
View File

@ -153,6 +153,7 @@ Format of STDIN stream:

#include "builtin.h"
#include "cache.h"
#include "lockfile.h"
#include "object.h"
#include "blob.h"
#include "tree.h"
@ -1832,10 +1833,8 @@ static void dump_marks(void)
}

if (commit_lock_file(&mark_lock)) {
int saved_errno = errno;
rollback_lock_file(&mark_lock);
failure |= error("Unable to commit marks file %s: %s",
export_marks_file, strerror(saved_errno));
export_marks_file, strerror(errno));
return;
}
}

1
fetch-pack.c
View File

@ -1,4 +1,5 @@
#include "cache.h"
#include "lockfile.h"
#include "refs.h"
#include "pkt-line.h"
#include "commit.h"

292
lockfile.c
View File

@ -2,59 +2,52 @@
* Copyright (c) 2005, Junio C Hamano
*/
#include "cache.h"
#include "lockfile.h"
#include "sigchain.h"

static struct lock_file *lock_file_list;
static struct lock_file *volatile lock_file_list;

static void remove_lock_file(void)
static void remove_lock_files(void)
{
pid_t me = getpid();

while (lock_file_list) {
if (lock_file_list->owner == me &&
lock_file_list->filename[0]) {
if (lock_file_list->fd >= 0)
close(lock_file_list->fd);
unlink_or_warn(lock_file_list->filename);
}
if (lock_file_list->owner == me)
rollback_lock_file(lock_file_list);
lock_file_list = lock_file_list->next;
}
}

static void remove_lock_file_on_signal(int signo)
static void remove_lock_files_on_signal(int signo)
{
remove_lock_file();
remove_lock_files();
sigchain_pop(signo);
raise(signo);
}

/*
* p = absolute or relative path name
* path = absolute or relative path name
*
* Return a pointer into p showing the beginning of the last path name
* element. If p is empty or the root directory ("/"), just return p.
* Remove the last path name element from path (leaving the preceding
* "/", if any). If path is empty or the root directory ("/"), set
* path to the empty string.
*/
static char *last_path_elm(char *p)
static void trim_last_path_component(struct strbuf *path)
{
/* r starts pointing to null at the end of the string */
char *r = strchr(p, '\0');

if (r == p)
return p; /* just return empty string */

r--; /* back up to last non-null character */
int i = path->len;

/* back up past trailing slashes, if any */
while (r > p && *r == '/')
r--;
while (i && path->buf[i - 1] == '/')
i--;

/*
* then go backwards until I hit a slash, or the beginning of
* the string
* then go backwards until a slash, or the beginning of the
* string
*/
while (r > p && *(r-1) != '/')
r--;
return r;
while (i && path->buf[i - 1] != '/')
i--;

strbuf_setlen(path, i);
}


@ -62,103 +55,87 @@ static char *last_path_elm(char *p)
#define MAXDEPTH 5

/*
* p = path that may be a symlink
* s = full size of p
* path contains a path that might be a symlink.
*
* If p is a symlink, attempt to overwrite p with a path to the real
* file or directory (which may or may not exist), following a chain of
* symlinks if necessary. Otherwise, leave p unmodified.
* If path is a symlink, attempt to overwrite it with a path to the
* real file or directory (which may or may not exist), following a
* chain of symlinks if necessary. Otherwise, leave path unmodified.
*
* This is a best-effort routine. If an error occurs, p will either be
* left unmodified or will name a different symlink in a symlink chain
* that started with p's initial contents.
*
* Always returns p.
* This is a best-effort routine. If an error occurs, path will
* either be left unmodified or will name a different symlink in a
* symlink chain that started with the original path.
*/

static char *resolve_symlink(char *p, size_t s)
static void resolve_symlink(struct strbuf *path)
{
int depth = MAXDEPTH;
static struct strbuf link = STRBUF_INIT;

while (depth--) {
char link[PATH_MAX];
int link_len = readlink(p, link, sizeof(link));
if (link_len < 0) {
/* not a symlink anymore */
return p;
}
else if (link_len < sizeof(link))
/* readlink() never null-terminates */
link[link_len] = '\0';
else {
warning("%s: symlink too long", p);
return p;
}
if (strbuf_readlink(&link, path->buf, path->len) < 0)
break;

if (is_absolute_path(link)) {
if (is_absolute_path(link.buf))
/* absolute path simply replaces p */
if (link_len < s)
strcpy(p, link);
else {
warning("%s: symlink too long", p);
return p;
}
} else {
strbuf_reset(path);
else
/*
* link is a relative path, so I must replace the
* link is a relative path, so replace the
* last element of p with it.
*/
char *r = (char *)last_path_elm(p);
if (r - p + link_len < s)
strcpy(r, link);
else {
warning("%s: symlink too long", p);
return p;
}
}
trim_last_path_component(path);

strbuf_addbuf(path, &link);
}
return p;
strbuf_reset(&link);
}

/* Make sure errno contains a meaningful value on error */
static int lock_file(struct lock_file *lk, const char *path, int flags)
{
/*
* subtract 5 from size to make sure there's room for adding
* ".lock" for the lock file name
*/
static const size_t max_path_len = sizeof(lk->filename) - 5;
size_t pathlen = strlen(path);

if (strlen(path) >= max_path_len) {
errno = ENAMETOOLONG;
if (!lock_file_list) {
/* One-time initialization */
sigchain_push_common(remove_lock_files_on_signal);
atexit(remove_lock_files);
}

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->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_add(&lk->filename, path, pathlen);
if (!(flags & LOCK_NO_DEREF))
resolve_symlink(&lk->filename);
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;
}
strcpy(lk->filename, path);
if (!(flags & LOCK_NODEREF))
resolve_symlink(lk->filename, max_path_len);
strcat(lk->filename, ".lock");
lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
if (0 <= lk->fd) {
if (!lock_file_list) {
sigchain_push_common(remove_lock_file_on_signal);
atexit(remove_lock_file);
}
lk->owner = getpid();
if (!lk->on_list) {
lk->next = lock_file_list;
lock_file_list = lk;
lk->on_list = 1;
}
if (adjust_shared_perm(lk->filename)) {
int save_errno = errno;
error("cannot fix permission bits on %s",
lk->filename);
errno = save_errno;
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;
}
else
lk->filename[0] = 0;
return lk->fd;
}

@ -185,7 +162,7 @@ int unable_to_lock_error(const char *path, int err)
return -1;
}

NORETURN void unable_to_lock_index_die(const char *path, int err)
NORETURN void unable_to_lock_die(const char *path, int err)
{
struct strbuf buf = STRBUF_INIT;

@ -198,7 +175,7 @@ int hold_lock_file_for_update(struct lock_file *lk, const char *path, int flags)
{
int fd = lock_file(lk, path, flags);
if (fd < 0 && (flags & LOCK_DIE_ON_ERROR))
unable_to_lock_index_die(path, errno);
unable_to_lock_die(path, errno);
return fd;
}

@ -209,23 +186,30 @@ int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
fd = lock_file(lk, path, flags);
if (fd < 0) {
if (flags & LOCK_DIE_ON_ERROR)
unable_to_lock_index_die(path, errno);
unable_to_lock_die(path, errno);
return fd;
}

orig_fd = open(path, O_RDONLY);
if (orig_fd < 0) {
if (errno != ENOENT) {
int save_errno = errno;

if (flags & LOCK_DIE_ON_ERROR)
die("cannot open '%s' for copying", path);
close(fd);
return error("cannot open '%s' for copying", path);
rollback_lock_file(lk);
error("cannot open '%s' for copying", path);
errno = save_errno;
return -1;
}
} else if (copy_fd(orig_fd, fd)) {
int save_errno = errno;

if (flags & LOCK_DIE_ON_ERROR)
exit(128);
close(orig_fd);
close(fd);
rollback_lock_file(lk);
errno = save_errno;
return -1;
} else {
close(orig_fd);
@ -233,52 +217,90 @@ int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
return fd;
}

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)
die("BUG: get_locked_file_path() called for malformed lock object");
return xmemdupz(lk->filename.buf, lk->filename.len - LOCK_SUFFIX_LEN);
}

int close_lock_file(struct lock_file *lk)
{
int fd = lk->fd;

if (fd < 0)
return 0;

lk->fd = -1;
return close(fd);
if (close(fd)) {
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->filename[0])
if (!lk->active)
die(_("BUG: reopen a lockfile that has been committed"));
lk->fd = open(lk->filename, O_WRONLY);
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;
}

int commit_lock_file(struct lock_file *lk)
{
char result_file[PATH_MAX];
size_t i;
if (lk->fd >= 0 && close_lock_file(lk))
return -1;
strcpy(result_file, lk->filename);
i = strlen(result_file) - 5; /* .lock */
result_file[i] = 0;
if (rename(lk->filename, result_file))
return -1;
lk->filename[0] = 0;
return 0;
}
static struct strbuf result_file = STRBUF_INIT;
int err;

int hold_locked_index(struct lock_file *lk, int die_on_error)
{
return hold_lock_file_for_update(lk, get_index_file(),
die_on_error
? LOCK_DIE_ON_ERROR
: 0);
if (!lk->active)
die("BUG: attempt to commit unlocked object");

if (lk->filename.len <= LOCK_SUFFIX_LEN ||
strcmp(lk->filename.buf + lk->filename.len - LOCK_SUFFIX_LEN, LOCK_SUFFIX))
die("BUG: lockfile filename corrupt");

/* remove ".lock": */
strbuf_add(&result_file, lk->filename.buf,
lk->filename.len - LOCK_SUFFIX_LEN);
err = commit_lock_file_to(lk, result_file.buf);
strbuf_reset(&result_file);
return err;
}

void rollback_lock_file(struct lock_file *lk)
{
if (lk->filename[0]) {
if (lk->fd >= 0)
close(lk->fd);
unlink_or_warn(lk->filename);
if (!lk->active)
return;

if (!close_lock_file(lk)) {
unlink_or_warn(lk->filename.buf);
lk->active = 0;
strbuf_reset(&lk->filename);
}
lk->filename[0] = 0;
}

84
lockfile.h Normal file
View File

@ -0,0 +1,84 @@
#ifndef LOCKFILE_H
#define LOCKFILE_H

/*
* File write-locks as used by Git.
*
* For an overview of how to use the lockfile API, please see
*
* Documentation/technical/api-lockfile.txt
*
* 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.
*
* A lockfile is owned by the process that created it. The lock_file
* object has an "owner" field that records its owner. This field is
* used to prevent a forked process from closing a lockfile created by
* its parent.
*
* 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 the 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
* - 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.
*/

struct lock_file {
struct lock_file *volatile next;
volatile sig_atomic_t active;
volatile int fd;
volatile pid_t owner;
char on_list;
struct strbuf filename;
};

/* String appended to a filename to derive the lockfile name: */
#define LOCK_SUFFIX ".lock"
#define LOCK_SUFFIX_LEN 5

#define LOCK_DIE_ON_ERROR 1
#define LOCK_NO_DEREF 2

extern int unable_to_lock_error(const char *path, int err);
extern void unable_to_lock_message(const char *path, int err,
struct strbuf *buf);
extern NORETURN void unable_to_lock_die(const char *path, int err);
extern int hold_lock_file_for_update(struct lock_file *, const char *path, int);
extern int hold_lock_file_for_append(struct lock_file *, const char *path, int);
extern char *get_locked_file_path(struct lock_file *);
extern int commit_lock_file_to(struct lock_file *, const char *path);
extern int commit_lock_file(struct lock_file *);
extern int reopen_lock_file(struct lock_file *);
extern int close_lock_file(struct lock_file *);
extern void rollback_lock_file(struct lock_file *);

#endif /* LOCKFILE_H */

1
merge-recursive.c
View File

@ -5,6 +5,7 @@
*/
#include "cache.h"
#include "advice.h"
#include "lockfile.h"
#include "cache-tree.h"
#include "commit.h"
#include "blob.h"

1
merge.c
View File

@ -1,4 +1,5 @@
#include "cache.h"
#include "lockfile.h"
#include "commit.h"
#include "run-command.h"
#include "resolve-undo.h"

21
read-cache.c
View File

@ -5,6 +5,7 @@
*/
#define NO_THE_INDEX_COMPATIBILITY_MACROS
#include "cache.h"
#include "lockfile.h"
#include "cache-tree.h"
#include "refs.h"
#include "dir.h"
@ -1367,6 +1368,14 @@ static int read_index_extension(struct index_state *istate,
return 0;
}

int hold_locked_index(struct lock_file *lk, int die_on_error)
{
return hold_lock_file_for_update(lk, get_index_file(),
die_on_error
? LOCK_DIE_ON_ERROR
: 0);
}

int read_index(struct index_state *istate)
{
return read_index_from(istate, get_index_file());
@ -2041,16 +2050,10 @@ void set_alternate_index_output(const char *name)

static int commit_locked_index(struct lock_file *lk)
{
if (alternate_index_output) {
if (lk->fd >= 0 && close_lock_file(lk))
return -1;
if (rename(lk->filename, alternate_index_output))
return -1;
lk->filename[0] = 0;
return 0;
} else {
if (alternate_index_output)
return commit_lock_file_to(lk, alternate_index_output);
else
return commit_lock_file(lk);
}
}

static int do_write_locked_index(struct index_state *istate, struct lock_file *lock,

23
refs.c
View File

@ -1,4 +1,5 @@
#include "cache.h"
#include "lockfile.h"
#include "refs.h"
#include "object.h"
#include "tag.h"
@ -79,7 +80,8 @@ out:
if (refname[1] == '\0')
return -1; /* Component equals ".". */
}
if (cp - refname >= 5 && !memcmp(cp - 5, ".lock", 5))
if (cp - refname >= LOCK_SUFFIX_LEN &&
!memcmp(cp - LOCK_SUFFIX_LEN, LOCK_SUFFIX, LOCK_SUFFIX_LEN))
return -1; /* Refname ends with ".lock". */
return cp - refname;
}
@ -2191,7 +2193,7 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
lflags = 0;
if (flags & REF_NODEREF) {
refname = orig_refname;
lflags |= LOCK_NODEREF;
lflags |= LOCK_NO_DEREF;
}
lock->ref_name = xstrdup(refname);
lock->orig_ref_name = xstrdup(orig_refname);
@ -2225,7 +2227,7 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
*/
goto retry;
else
unable_to_lock_index_die(ref_file, errno);
unable_to_lock_die(ref_file, errno);
}
return old_sha1 ? verify_lock(lock, old_sha1, mustexist) : lock;

@ -2601,12 +2603,13 @@ int repack_without_refs(const char **refnames, int n, struct strbuf *err)
static int delete_ref_loose(struct ref_lock *lock, int flag)
{
if (!(flag & REF_ISPACKED) || flag & REF_ISSYMREF) {
/* loose */
int err, i = strlen(lock->lk->filename) - 5; /* .lock */

lock->lk->filename[i] = 0;
err = unlink_or_warn(lock->lk->filename);
lock->lk->filename[i] = '.';
/*
* loose. The loose file name is the same as the
* lockfile name, minus ".lock":
*/
char *loose_filename = get_locked_file_path(lock->lk);
int err = unlink_or_warn(loose_filename);
free(loose_filename);
if (err && errno != ENOENT)
return 1;
}
@ -2968,7 +2971,7 @@ int write_ref_sha1(struct ref_lock *lock,
write_in_full(lock->lock_fd, &term, 1) != 1 ||
close_ref(lock) < 0) {
int save_errno = errno;
error("Couldn't write %s", lock->lk->filename);
error("Couldn't write %s", lock->lk->filename.buf);
unlock_ref(lock);
errno = save_errno;
return -1;

1
rerere.c
View File

@ -1,4 +1,5 @@
#include "cache.h"
#include "lockfile.h"
#include "string-list.h"
#include "rerere.h"
#include "xdiff-interface.h"

1
sequencer.c
View File

@ -1,4 +1,5 @@
#include "cache.h"
#include "lockfile.h"
#include "sequencer.h"
#include "dir.h"
#include "object.h"

1
sha1_file.c
View File

@ -8,6 +8,7 @@
*/
#include "cache.h"
#include "string-list.h"
#include "lockfile.h"
#include "delta.h"
#include "pack.h"
#include "blob.h"

7
shallow.c
View File

@ -1,4 +1,5 @@
#include "cache.h"
#include "lockfile.h"
#include "commit.h"
#include "tag.h"
#include "pkt-line.h"
@ -269,8 +270,8 @@ void setup_alternate_shallow(struct lock_file *shallow_lock,
if (write_shallow_commits(&sb, 0, extra)) {
if (write_in_full(fd, sb.buf, sb.len) != sb.len)
die_errno("failed to write to %s",
shallow_lock->filename);
*alternate_shallow_file = shallow_lock->filename;
shallow_lock->filename.buf);
*alternate_shallow_file = shallow_lock->filename.buf;
} else
/*
* is_repository_shallow() sees empty string as "no
@ -316,7 +317,7 @@ void prune_shallow(int show_only)
if (write_shallow_commits_1(&sb, 0, NULL, SEEN_ONLY)) {
if (write_in_full(fd, sb.buf, sb.len) != sb.len)
die_errno("failed to write to %s",
shallow_lock.filename);
shallow_lock.filename.buf);
commit_lock_file(&shallow_lock);
} else {
unlink(git_path("shallow"));

1
test-scrap-cache-tree.c
View File

@ -1,4 +1,5 @@
#include "cache.h"
#include "lockfile.h"
#include "tree.h"
#include "cache-tree.h"