lockfile.h: extract new header file for the functions in lockfile.c
[git/git.git] / lockfile.h
1 #ifndef LOCKFILE_H
2 #define LOCKFILE_H
3
4 /*
5 * File write-locks as used by Git.
6 *
7 * For an overview of how to use the lockfile API, please see
8 *
9 * Documentation/technical/api-lockfile.txt
10 *
11 * This module keeps track of all locked files in lock_file_list for
12 * use at cleanup. This list and the lock_file objects that comprise
13 * it must be kept in self-consistent states at all time, because the
14 * program can be interrupted any time by a signal, in which case the
15 * signal handler will walk through the list attempting to clean up
16 * any open lock files.
17 *
18 * A lockfile is owned by the process that created it. The lock_file
19 * object has an "owner" field that records its owner. This field is
20 * used to prevent a forked process from closing a lockfile created by
21 * its parent.
22 *
23 * The possible states of a lock_file object are as follows:
24 *
25 * - Uninitialized. In this state the object's on_list field must be
26 * zero but the rest of its contents need not be initialized. As
27 * soon as the object is used in any way, it is irrevocably
28 * registered in the lock_file_list, and on_list is set.
29 *
30 * - Locked, lockfile open (after hold_lock_file_for_update(),
31 * hold_lock_file_for_append(), or reopen_lock_file()). In this
32 * state:
33 * - the lockfile exists
34 * - active is set
35 * - filename holds the filename of the lockfile
36 * - fd holds a file descriptor open for writing to the lockfile
37 * - owner holds the PID of the process that locked the file
38 *
39 * - Locked, lockfile closed (after successful close_lock_file()).
40 * Same as the previous state, except that the lockfile is closed
41 * and fd is -1.
42 *
43 * - Unlocked (after commit_lock_file(), commit_lock_file_to(),
44 * rollback_lock_file(), a failed attempt to lock, or a failed
45 * close_lock_file()). In this state:
46 * - active is unset
47 * - filename is empty (usually, though there are transitory
48 * states in which this condition doesn't hold). Client code should
49 * *not* rely on the filename being empty in this state.
50 * - fd is -1
51 * - the object is left registered in the lock_file_list, and
52 * on_list is set.
53 */
54
55 struct lock_file {
56 struct lock_file *volatile next;
57 volatile sig_atomic_t active;
58 volatile int fd;
59 volatile pid_t owner;
60 char on_list;
61 struct strbuf filename;
62 };
63
64 /* String appended to a filename to derive the lockfile name: */
65 #define LOCK_SUFFIX ".lock"
66 #define LOCK_SUFFIX_LEN 5
67
68 #define LOCK_DIE_ON_ERROR 1
69 #define LOCK_NO_DEREF 2
70
71 extern int unable_to_lock_error(const char *path, int err);
72 extern void unable_to_lock_message(const char *path, int err,
73 struct strbuf *buf);
74 extern NORETURN void unable_to_lock_die(const char *path, int err);
75 extern int hold_lock_file_for_update(struct lock_file *, const char *path, int);
76 extern int hold_lock_file_for_append(struct lock_file *, const char *path, int);
77 extern char *get_locked_file_path(struct lock_file *);
78 extern int commit_lock_file_to(struct lock_file *, const char *path);
79 extern int commit_lock_file(struct lock_file *);
80 extern int reopen_lock_file(struct lock_file *);
81 extern int close_lock_file(struct lock_file *);
82 extern void rollback_lock_file(struct lock_file *);
83
84 #endif /* LOCKFILE_H */