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+#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 */