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authorJoern Engel <joern@wohnheim.fh-wedel.de>2007-10-16 23:30:44 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-17 08:43:02 -0700
commit1c0eeaf5698597146ed9b873e2f9e0961edcf0f9 (patch)
tree5265eac8437e8ce517a62db8fe2bd99db5b7019b /include/linux/fs.h
parent2e6883bdf49abd0e7f0d9b6297fc3be7ebb2250b (diff)
introduce I_SYNC
I_LOCK was used for several unrelated purposes, which caused deadlock situations in certain filesystems as a side effect. One of the purposes now uses the new I_SYNC bit. Also document the various bits and change their order from historical to logical. [bunk@stusta.de: make fs/inode.c:wake_up_inode() static] Signed-off-by: Joern Engel <joern@wohnheim.fh-wedel.de> Cc: Dave Kleikamp <shaggy@linux.vnet.ibm.com> Cc: David Chinner <dgc@sgi.com> Cc: Anton Altaparmakov <aia21@cam.ac.uk> Cc: Al Viro <viro@ftp.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/fs.h')
-rw-r--r--include/linux/fs.h70
1 files changed, 61 insertions, 9 deletions
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b70331f9f5b7..365586a4c4de 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1261,16 +1261,68 @@ struct super_operations {
#endif
};
-/* Inode state bits. Protected by inode_lock. */
-#define I_DIRTY_SYNC 1 /* Not dirty enough for O_DATASYNC */
-#define I_DIRTY_DATASYNC 2 /* Data-related inode changes pending */
-#define I_DIRTY_PAGES 4 /* Data-related inode changes pending */
-#define __I_LOCK 3
+/*
+ * Inode state bits. Protected by inode_lock.
+ *
+ * Three bits determine the dirty state of the inode, I_DIRTY_SYNC,
+ * I_DIRTY_DATASYNC and I_DIRTY_PAGES.
+ *
+ * Four bits define the lifetime of an inode. Initially, inodes are I_NEW,
+ * until that flag is cleared. I_WILL_FREE, I_FREEING and I_CLEAR are set at
+ * various stages of removing an inode.
+ *
+ * Two bits are used for locking and completion notification, I_LOCK and I_SYNC.
+ *
+ * I_DIRTY_SYNC Inode itself is dirty.
+ * I_DIRTY_DATASYNC Data-related inode changes pending
+ * I_DIRTY_PAGES Inode has dirty pages. Inode itself may be clean.
+ * I_NEW get_new_inode() sets i_state to I_LOCK|I_NEW. Both
+ * are cleared by unlock_new_inode(), called from iget().
+ * I_WILL_FREE Must be set when calling write_inode_now() if i_count
+ * is zero. I_FREEING must be set when I_WILL_FREE is
+ * cleared.
+ * I_FREEING Set when inode is about to be freed but still has dirty
+ * pages or buffers attached or the inode itself is still
+ * dirty.
+ * I_CLEAR Set by clear_inode(). In this state the inode is clean
+ * and can be destroyed.
+ *
+ * Inodes that are I_WILL_FREE, I_FREEING or I_CLEAR are
+ * prohibited for many purposes. iget() must wait for
+ * the inode to be completely released, then create it
+ * anew. Other functions will just ignore such inodes,
+ * if appropriate. I_LOCK is used for waiting.
+ *
+ * I_LOCK Serves as both a mutex and completion notification.
+ * New inodes set I_LOCK. If two processes both create
+ * the same inode, one of them will release its inode and
+ * wait for I_LOCK to be released before returning.
+ * Inodes in I_WILL_FREE, I_FREEING or I_CLEAR state can
+ * also cause waiting on I_LOCK, without I_LOCK actually
+ * being set. find_inode() uses this to prevent returning
+ * nearly-dead inodes.
+ * I_SYNC Similar to I_LOCK, but limited in scope to writeback
+ * of inode dirty data. Having a seperate lock for this
+ * purpose reduces latency and prevents some filesystem-
+ * specific deadlocks.
+ *
+ * Q: Why does I_DIRTY_DATASYNC exist? It appears as if it could be replaced
+ * by (I_DIRTY_SYNC|I_DIRTY_PAGES).
+ * Q: What is the difference between I_WILL_FREE and I_FREEING?
+ * Q: igrab() only checks on (I_FREEING|I_WILL_FREE). Should it also check on
+ * I_CLEAR? If not, why?
+ */
+#define I_DIRTY_SYNC 1
+#define I_DIRTY_DATASYNC 2
+#define I_DIRTY_PAGES 4
+#define I_NEW 8
+#define I_WILL_FREE 16
+#define I_FREEING 32
+#define I_CLEAR 64
+#define __I_LOCK 7
#define I_LOCK (1 << __I_LOCK)
-#define I_FREEING 16
-#define I_CLEAR 32
-#define I_NEW 64
-#define I_WILL_FREE 128
+#define __I_SYNC 8
+#define I_SYNC (1 << __I_SYNC)
#define I_DIRTY (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_PAGES)