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- Lock-ahead translator
- ---------------------
-
-The objective of the lock-ahead translator is to speculatively
-hold locks (inodelk and entrylk) on the universal set (0 - infinity
-in case of inodelk and all basenames in case of entrylk) even
-when a lock is requested only on a subset, in anticipation that
-further locks will be requested within the same universal set.
-
-So, for example, when cluster/replicate locks a region before
-writing to it, lock-ahead would instead lock the entire file.
-On further writes, lock-ahead can immediately return success for
-the lock requests, since the entire file has been previously locked.
-
-To avoid starvation of other clients/mountpoints, we employ a
-notify mechanism, described below.
-
-typedef struct {
- struct list_head subset_locks;
-} la_universal_lock_t;
-
-Universal lock structure is stored in the inode context.
-
-typedef struct {
- enum {LOCK_AHEAD_ENTRYLK, LOCK_AHEAD_FENTRYLK,
- LOCK_AHEAD_INODELK, LOCK_AHEAD_FINODELK};
-
- union {
- fd_t *fd;
- loc_t loc;
- };
-
- off_t l_start;
- off_t l_len;
-
- const char *basename;
-
- struct list_head universal_lock;
-} la_subset_lock_t;
-
-
-fops implemented:
-
-* inodelk/finodelk/entrylk/fentrylk:
-
-lock:
- if universal lock held:
- add subset to it (save loc_t or fd) and return success
- else:
- send lock-notify fop
- hold universal lock and return
- (set inode context, add subset to it, save loc_t or fd)
-
- if this fails:
- forward the lock request
-
-unlock:
- if subset exists in universal lock:
- delete subset lock from list
- else:
- forward it
-
-* release:
- hold subset locks (each subset lock using the saved loc_t or fd)
- and release universal lock
-
-* lock-notify (on unwind) (new fop)
- hold subset locks and release universal lock
-
-
-lock-notify in locks translator:
-
-if a subset lock in entrylk/inodelk cannot be satisfied
-because of a universal lock held by someone else:
- unwind the lock-notify fop
-
-==============================================
-$ Last updated: Tue Feb 17 11:31:18 IST 2009 $
-$ Author: Vikas Gorur <vikas@gluster.com> $
-==============================================