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Date: Mon, 15 Sep 2008 12:36:48 -0700
From: Abhijit Paithankar <apaithan@...mai.com>
To: Andreas Dilger <adilger@....com>
Cc: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
Jamie Lokier <jamie@...reable.org>,
Dave Chinner <david@...morbit.com>
Subject: Re: [RFC PATCH] Filesystem Journal Notifications
Thanks for your feedback.
It gave me new points to think about.
I have used inotify simply because it is a mechanism that already exists
in the kernel and is easily extensible.
The use of transaction ids as "journal cookie" was done to simplify
things. A journal transaction ID is a readily available monotonically
increasing ID unique to that partition (super block).
Journal cookies themselves are completely opaque to the application
and as long as it is a monotonically increasing number that signifies
a journal commit, it could be anything that a file system chooses it
to be.
Ext3/Ext4 gather multiple changes into a single transaction. So,
you will see a single 'commit' notification for multiple of meta-data
changes. The 'commit' messages, therefore, won't be that many.
This patch (v2):
In this version of the patch I've done away with most of the file-system
specific changes. The file system now only needs to send out a journal
commit notification.
The 'journal cookie' is simply a u64 that increases every time a journal
'commit' is made. This will make the code more portable to other file
systems.
Also, we no longer need those many journal message types. We can easily
piggy-back on top of fsnotify. The only remaining one is
IN_JOURNAL_COMMIT.
My next step is to allow multiple registrations for JOURNAL_COMMIT
notification. I will post that patch once it is ready.
Signed-off-by: Abhijit Paithankar <apaithan@...mai.com>
---
fs/ext3/ext3_jbd.c | 9 +++++
fs/ext4/ext4_jbd2.c | 9 +++++
fs/inotify.c | 17 ++++++---
fs/inotify_user.c | 81 ++++++++++++++++++++++++++++++++++++++++++-----
fs/jbd/commit.c | 1
fs/jbd2/commit.c | 1
include/linux/fs.h | 2 +
include/linux/fsnotify.h | 11 ++++++
include/linux/inotify.h | 19 ++++++++++-
include/linux/jbd.h | 1
include/linux/jbd2.h | 1
11 files changed, 138 insertions(+), 14 deletions(-)
---
Index: linux-2.6/fs/ext3/ext3_jbd.c
===================================================================
--- linux-2.6.orig/fs/ext3/ext3_jbd.c 2008-09-15 10:12:25.000000000 -0700
+++ linux-2.6/fs/ext3/ext3_jbd.c 2008-09-15 10:15:54.000000000 -0700
@@ -3,6 +3,7 @@
*/
#include <linux/ext3_jbd.h>
+#include <linux/fsnotify.h>
int __ext3_journal_get_undo_access(const char *where, handle_t *handle,
struct buffer_head *bh)
@@ -57,3 +58,11 @@
ext3_journal_abort_handle(where, __func__, bh, handle,err);
return err;
}
+
+void journal_notify_commit (journal_t *journal)
+{
+ struct super_block *sb = journal->j_private;
+ if (sb->s_priv_inode && sb->s_journal_cookie)
+ fsnotify_journal_commit(sb);
+}
+
Index: linux-2.6/fs/ext4/ext4_jbd2.c
===================================================================
--- linux-2.6.orig/fs/ext4/ext4_jbd2.c 2008-09-15 10:14:12.000000000 -0700
+++ linux-2.6/fs/ext4/ext4_jbd2.c 2008-09-15 10:15:50.000000000 -0700
@@ -2,6 +2,7 @@
* Interface between ext4 and JBD
*/
+#include <linux/fsnotify.h>
#include "ext4_jbd2.h"
int __ext4_journal_get_undo_access(const char *where, handle_t *handle,
@@ -57,3 +58,11 @@
ext4_journal_abort_handle(where, __func__, bh, handle, err);
return err;
}
+
+void jbd2_journal_notify_commit (journal_t *journal)
+{
+ struct super_block *sb = journal->j_private;
+ if (sb->s_priv_inode && sb->s_journal_cookie)
+ fsnotify_journal_commit(sb);
+}
+
Index: linux-2.6/fs/inotify.c
===================================================================
--- linux-2.6.orig/fs/inotify.c 2008-09-15 10:12:29.000000000 -0700
+++ linux-2.6/fs/inotify.c 2008-09-15 10:13:44.000000000 -0700
@@ -231,7 +231,7 @@
struct inotify_watch *watch)
{
remove_watch_no_event(watch, ih);
- ih->in_ops->handle_event(watch, watch->wd, IN_IGNORED, 0, NULL, NULL);
+ ih->in_ops->handle_event(watch, watch->wd, IN_IGNORED, 0, NULL, NULL, 0);
}
EXPORT_SYMBOL_GPL(inotify_remove_watch_locked);
@@ -280,10 +280,17 @@
const char *name, struct inode *n_inode)
{
struct inotify_watch *watch, *next;
+ u64 journal_cookie = 0;
if (!inotify_inode_watched(inode))
return;
+ if (mask & (IN_ATTRIB | IN_MOVE | IN_CREATE | IN_DELETE |
+ IN_DELETE_SELF | IN_MOVE_SELF)) {
+ if (inode->i_sb && inode->i_sb->s_journal_cookie)
+ journal_cookie = inode->i_sb->s_journal_cookie;
+ }
+
mutex_lock(&inode->inotify_mutex);
list_for_each_entry_safe(watch, next, &inode->inotify_watches, i_list) {
u32 watch_mask = watch->mask;
@@ -293,7 +300,7 @@
if (watch_mask & IN_ONESHOT)
remove_watch_no_event(watch, ih);
ih->in_ops->handle_event(watch, watch->wd, mask, cookie,
- name, n_inode);
+ name, n_inode, journal_cookie);
mutex_unlock(&ih->mutex);
}
}
@@ -409,7 +416,7 @@
struct inotify_handle *ih= watch->ih;
mutex_lock(&ih->mutex);
ih->in_ops->handle_event(watch, watch->wd, IN_UNMOUNT, 0,
- NULL, NULL);
+ NULL, NULL, 0);
inotify_remove_watch_locked(ih, watch);
mutex_unlock(&ih->mutex);
}
@@ -576,7 +583,7 @@
mask_add = 1;
/* don't allow invalid bits: we don't want flags set */
- mask &= IN_ALL_EVENTS | IN_ONESHOT;
+ mask &= IN_ALL_EVENTS | IN_ONESHOT | IN_JOURNAL_COMMIT;
if (unlikely(!mask))
return -EINVAL;
@@ -623,7 +630,7 @@
int newly_watched;
/* don't allow invalid bits: we don't want flags set */
- mask &= IN_ALL_EVENTS | IN_ONESHOT;
+ mask &= IN_ALL_EVENTS | IN_ONESHOT | IN_JOURNAL_COMMIT;
if (unlikely(!mask))
return -EINVAL;
watch->mask = mask;
Index: linux-2.6/fs/inotify_user.c
===================================================================
--- linux-2.6.orig/fs/inotify_user.c 2008-09-15 10:12:34.000000000 -0700
+++ linux-2.6/fs/inotify_user.c 2008-09-15 10:51:43.000000000 -0700
@@ -185,7 +185,7 @@
* This function can sleep.
*/
static struct inotify_kernel_event * kernel_event(s32 wd, u32 mask, u32 cookie,
- const char *name)
+ const char *name, u64 journal_cookie)
{
struct inotify_kernel_event *kevent;
@@ -204,6 +204,7 @@
if (name) {
size_t len, rem, event_size = sizeof(struct inotify_event);
+ size_t journal_cookie_sz;
/*
* We need to pad the filename so as to properly align an
@@ -213,6 +214,10 @@
* simple and safe for all architectures.
*/
len = strlen(name) + 1;
+ if (journal_cookie) {
+ journal_cookie_sz = sizeof(u64);
+ len = len + journal_cookie_sz;
+ }
rem = event_size - len;
if (len > event_size) {
rem = event_size - (len % event_size);
@@ -225,13 +230,52 @@
kmem_cache_free(event_cachep, kevent);
return NULL;
}
- memcpy(kevent->name, name, len);
+ if (journal_cookie) {
+ char *ch;
+
+ memcpy(kevent->name, name, strlen(name));
+ ch = kevent->name;
+ ch += strlen(name);
+ memset(ch++, 0, 1);
+ sprintf(ch, "%llu", journal_cookie);
+ }
+ else {
+ memcpy(kevent->name, name, len);
+ }
if (rem)
memset(kevent->name + len, 0, rem);
kevent->event.len = len + rem;
} else {
- kevent->event.len = 0;
- kevent->name = NULL;
+ if (journal_cookie) {
+ size_t len, rem, event_size = sizeof(struct inotify_event);
+ size_t journal_cookie_sz = sizeof(u64);
+ char *ch;
+
+ len = 1 + journal_cookie_sz;
+ rem = event_size - len;
+ if (len > event_size) {
+ rem = event_size - (len % event_size);
+ if (len % event_size == 0)
+ rem = 0;
+ }
+
+ kevent->name = kmalloc(len + rem, GFP_KERNEL);
+ if (unlikely(!kevent->name)) {
+ kmem_cache_free(event_cachep, kevent);
+ return NULL;
+ }
+ memset(kevent->name, 0, 1);
+ ch = kevent->name;
+ ch += 1;
+ sprintf(ch, "%llu", journal_cookie);
+ if (rem)
+ memset(kevent->name + len, 0, rem);
+ kevent->event.len = len + rem;
+ }
+ else {
+ kevent->event.len = 0;
+ kevent->name = NULL;
+ }
}
return kevent;
@@ -269,7 +313,7 @@
*/
static void inotify_dev_queue_event(struct inotify_watch *w, u32 wd, u32 mask,
u32 cookie, const char *name,
- struct inode *ignored)
+ struct inode *ignored, u64 journal_cookie)
{
struct inotify_user_watch *watch;
struct inotify_device *dev;
@@ -280,11 +324,25 @@
mutex_lock(&dev->ev_mutex);
+ if (mask & IN_JOURNAL_COMMIT) {
+ if (!(w->inode) || !(w->inode->i_sb)
+ || !(w->inode->i_sb->s_priv_inode)
+ || !(w->inode->i_sb->s_journal_cookie))
+ goto out;
+ }
/* we can safely put the watch as we don't reference it while
* generating the event
*/
- if (mask & IN_IGNORED || w->mask & IN_ONESHOT)
+ if (mask & IN_IGNORED || w->mask & IN_ONESHOT) {
+ if (w->mask & IN_JOURNAL_COMMIT) {
+ struct super_block *sb = NULL;
+ if (w->inode && w->inode->i_sb)
+ sb = w->inode->i_sb;
+ if (sb && sb->s_priv_inode)
+ sb->s_priv_inode = NULL;
+ }
put_inotify_watch(w); /* final put */
+ }
/* coalescing: drop this event if it is a dupe of the previous */
last = inotify_dev_get_last_event(dev);
@@ -304,9 +362,9 @@
/* if the queue overflows, we need to notify user space */
if (unlikely(dev->event_count == dev->max_events))
- kevent = kernel_event(-1, IN_Q_OVERFLOW, cookie, NULL);
+ kevent = kernel_event(-1, IN_Q_OVERFLOW, cookie, NULL, 0);
else
- kevent = kernel_event(wd, mask, cookie, name);
+ kevent = kernel_event(wd, mask, cookie, name, journal_cookie);
if (unlikely(!kevent))
goto out;
@@ -686,6 +744,13 @@
ret = inotify_find_update_watch(dev->ih, inode, mask);
if (ret == -ENOENT)
ret = create_watch(dev, inode, mask);
+ if (ret >= 0) {
+ if (mask & IN_JOURNAL_COMMIT) {
+ struct super_block *sb = inode->i_sb;
+ if (sb)
+ sb->s_priv_inode = inode;
+ }
+ }
mutex_unlock(&dev->up_mutex);
path_put(&path);
Index: linux-2.6/fs/jbd/commit.c
===================================================================
--- linux-2.6.orig/fs/jbd/commit.c 2008-09-15 10:12:42.000000000 -0700
+++ linux-2.6/fs/jbd/commit.c 2008-09-15 10:13:44.000000000 -0700
@@ -928,6 +928,7 @@
}
spin_unlock(&journal->j_list_lock);
+ journal_notify_commit(journal);
jbd_debug(1, "JBD: commit %d complete, head %d\n",
journal->j_commit_sequence, journal->j_tail_sequence);
Index: linux-2.6/fs/jbd2/commit.c
===================================================================
--- linux-2.6.orig/fs/jbd2/commit.c 2008-09-15 10:14:00.000000000 -0700
+++ linux-2.6/fs/jbd2/commit.c 2008-09-15 10:16:09.000000000 -0700
@@ -990,6 +990,7 @@
}
spin_unlock(&journal->j_list_lock);
+ jbd2_journal_notify_commit(journal);
jbd_debug(1, "JBD: commit %d complete, head %d\n",
journal->j_commit_sequence, journal->j_tail_sequence);
Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h 2008-09-15 10:12:47.000000000 -0700
+++ linux-2.6/include/linux/fs.h 2008-09-15 10:13:44.000000000 -0700
@@ -1106,6 +1106,8 @@
char s_id[32]; /* Informational name */
void *s_fs_info; /* Filesystem private info */
+ u64 s_journal_cookie; /* current journal cookie # */
+ struct inode *s_priv_inode; /* used for journal notifications */
/*
* The next field is for VFS *only*. No filesystems have any business
Index: linux-2.6/include/linux/fsnotify.h
===================================================================
--- linux-2.6.orig/include/linux/fsnotify.h 2008-09-15 10:12:53.000000000 -0700
+++ linux-2.6/include/linux/fsnotify.h 2008-09-15 10:13:44.000000000 -0700
@@ -34,6 +34,17 @@
inotify_d_move(entry);
}
+static inline void fsnotify_journal_commit (struct super_block *sb)
+{
+ struct inode *inode;
+ sb->s_journal_cookie += 1;
+ if (sb->s_journal_cookie && sb->s_priv_inode) {
+ inode = sb->s_priv_inode;
+ inotify_inode_queue_event(inode, IN_JOURNAL_COMMIT, 0,
+ NULL, NULL);
+ }
+}
+
/*
* fsnotify_move - file old_name at old_dir was moved to new_name at new_dir
*/
Index: linux-2.6/include/linux/inotify.h
===================================================================
--- linux-2.6.orig/include/linux/inotify.h 2008-09-15 10:12:59.000000000 -0700
+++ linux-2.6/include/linux/inotify.h 2008-09-15 10:13:44.000000000 -0700
@@ -44,6 +44,23 @@
#define IN_Q_OVERFLOW 0x00004000 /* Event queued overflowed */
#define IN_IGNORED 0x00008000 /* File was ignored */
+/* This is a journal commit event for file systems. These events are sent
+ * from a journaling filesystem or the journal itself.
+ *
+ * IN_JOURNAL_COMMIT is special in that only one file per journaling filesystem
+ * partition (super-block) is allowed. Registering for this event with multiple
+ * files will overwrite previous registrations. The last registration for this
+ * event will be taken as current and commit notifications will be delivered
+ * for that inode only.
+ *
+ * The inode registered for this event should not be unlinked. This will disable
+ * any further journal commit notifications.
+ *
+ * If this event is not registered for, journal commit messages will not be
+ * delivered
+ */
+#define IN_JOURNAL_COMMIT 0x00010000 /* Journal on this superblock has committed a transaction */
+
/* helper events */
#define IN_CLOSE (IN_CLOSE_WRITE | IN_CLOSE_NOWRITE) /* close */
#define IN_MOVE (IN_MOVED_FROM | IN_MOVED_TO) /* moves */
@@ -97,7 +114,7 @@
struct inotify_operations {
void (*handle_event)(struct inotify_watch *, u32, u32, u32,
- const char *, struct inode *);
+ const char *, struct inode *, u64);
void (*destroy_watch)(struct inotify_watch *);
};
Index: linux-2.6/include/linux/jbd.h
===================================================================
--- linux-2.6.orig/include/linux/jbd.h 2008-09-15 10:13:08.000000000 -0700
+++ linux-2.6/include/linux/jbd.h 2008-09-15 10:13:44.000000000 -0700
@@ -114,6 +114,7 @@
* This is an opaque datatype.
**/
typedef struct journal_s journal_t; /* Journal control structure */
+extern void journal_notify_commit(journal_t *journal);
#endif
/*
Index: linux-2.6/include/linux/jbd2.h
===================================================================
--- linux-2.6.orig/include/linux/jbd2.h 2008-09-15 10:16:18.000000000 -0700
+++ linux-2.6/include/linux/jbd2.h 2008-09-15 10:16:45.000000000 -0700
@@ -115,6 +115,7 @@
* This is an opaque datatype.
**/
typedef struct journal_s journal_t; /* Journal control structure */
+extern void jbd2_journal_notify_commit(journal_t *journal);
#endif
/*
--
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