[PATCH 3/3][RFC](Repost) ext4: add a message in remount/umount for ext4

[PATCH 3/3][RFC](Repost) ext4: add a message in remount/umount for ext4

[Toshiyuki Okajima]

From: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>

ext4 doesn't log a record of having unmounted the filesystem. And ext4 doesn't 
log a record when the filesystem is remounted also with read-only. Therefore 
in the system log, we cannot judge whether or not at the certain time this
filesystem user touches it.
For enterprise users, they often want to know when a certain filesystem is 
mounted/remounted/unmounted.

So, we output the message to the system log when the filesystem is 
remounted/unmounted.

Signed-off-by: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>
---
 fs/ext4/super.c |   30 ++++++++++++++++++++++--------
 1 file changed, 22 insertions(+), 8 deletions(-)

diff -Nurp linux-2.6.31.orig/fs/ext4/super.c linux-2.6.31/fs/ext4/super.c
--- linux-2.6.31.orig/fs/ext4/super.c	2009-09-10 07:13:59.000000000 +0900
+++ linux-2.6.31/fs/ext4/super.c	2009-09-11 17:11:07.000000000 +0900
@@ -508,6 +508,25 @@ void ext4_update_dynamic_rev(struct supe
 	 */
 }
 
+static void ext4_print_mount_message(struct super_block *sb, 
+					int is_remount)
+{
+	if (EXT4_SB(sb)->s_journal) {
+		ext4_msg(sb, KERN_INFO, "%s, %s journal on %s",
+			is_remount? "remounted": "mounted",
+		       EXT4_SB(sb)->s_journal->j_inode ? "internal" :
+		       "external", EXT4_SB(sb)->s_journal->j_devname);
+	} else {
+		ext4_msg(sb, KERN_INFO, "%s, no journal",
+				is_remount? "remounted": "mounted");
+	}
+}
+
+static void ext4_print_umount_message(struct super_block *sb)
+{
+	ext4_msg(sb, KERN_INFO, "unmounted");
+}
+
 /*
  * Open the external journal device
  */
@@ -645,6 +664,7 @@ static void ext4_put_super(struct super_
 	 * Now that we are completely done shutting down the
 	 * superblock, we need to actually destroy the kobject.
 	 */
+	ext4_print_umount_message(sb);
 	unlock_kernel();
 	unlock_super(sb);
 	kobject_put(&sbi->s_kobj);
@@ -1645,14 +1665,6 @@ static int ext4_setup_super(struct super
 			EXT4_BLOCKS_PER_GROUP(sb),
 			EXT4_INODES_PER_GROUP(sb),
 			sbi->s_mount_opt);
-
-	if (EXT4_SB(sb)->s_journal) {
-		ext4_msg(sb, KERN_INFO, "%s journal on %s",
-		       EXT4_SB(sb)->s_journal->j_inode ? "internal" :
-		       "external", EXT4_SB(sb)->s_journal->j_devname);
-	} else {
-		ext4_msg(sb, KERN_INFO, "no journal");
-	}
 	return res;
 }
 
@@ -2806,6 +2818,7 @@ no_journal:
 	}
 
 	ext4_setup_super(sb, es, sb->s_flags & MS_RDONLY);
+	ext4_print_mount_message(sb, 0);
 
 	/* determine the minimum size of new large inodes, if present */
 	if (sbi->s_inode_size > EXT4_GOOD_OLD_INODE_SIZE) {
@@ -3547,6 +3560,7 @@ static int ext4_remount(struct super_blo
 		    old_opts.s_qf_names[i] != sbi->s_qf_names[i])
 			kfree(old_opts.s_qf_names[i]);
 #endif
+	ext4_print_mount_message(sb, 1);
 	unlock_super(sb);
 	unlock_kernel();
 	return 0;

Re: [PATCH 3/3][RFC](Repost) ext4: add a message in remount/umount for ext4

[Theodore Tso]

On Wed, Sep 30, 2009 at 03:49:31PM +0900, Toshiyuki Okajima wrote:
> From: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>
> 
> ext4 doesn't log a record of having unmounted the filesystem. And ext4 doesn't 
> log a record when the filesystem is remounted also with read-only. Therefore 
> in the system log, we cannot judge whether or not at the certain time this
> filesystem user touches it.
> For enterprise users, they often want to know when a certain filesystem is 
> mounted/remounted/unmounted.
> 
> So, we output the message to the system log when the filesystem is 
> remounted/unmounted.
> 
> Signed-off-by: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>

The question of whether this should be at the VFS layer is still an
open one, I think.  It is true that ext3 and ext4 does print some
filesystem specific information, but that could be handled via a new
method function in struct super_ops:

       mount_msg(struct super *sb, char *buf, int buflen)

Note by the way that I've made some changes to clean up ext4's
mount/umount messages, trying to get rid of excess messages.  In fact
ext4 already prints a "filesystem mounted" message in
ext4_fill_super().  You removed the one in ext4_setup_super(), but
I've already removed it in a recent commit pushed to Linus to remove
superflous mount-time printk's.  I left the one at the very end of
ext4_fill_super() in; and your patch adds one about 2/3'rd of the way
into ext4_fill_super() --- so two "filesystem mounted" messages would
end up getting printed as a result.  

Did you actually test the patch and see what sort of messages would be
printed as a result?

						- Ted

Re: [PATCH 3/3][RFC](Repost) ext4: add a message in remount/umount for ext4

[Toshiyuki Okajima]

Hi Ted, thank you for your comment.

Theodore Tso wrote:
 > On Wed, Sep 30, 2009 at 03:49:31PM +0900, Toshiyuki Okajima wrote:
 > > > From: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>
 > > >
 > > > ext4 doesn't log a record of having unmounted the filesystem. And ext4 doesn't
 > > > log a record when the filesystem is remounted also with read-only. Therefore
 > > > in the system log, we cannot judge whether or not at the certain time this
 > > > filesystem user touches it.
 > > > For enterprise users, they often want to know when a certain filesystem is
 > > > mounted/remounted/unmounted.
 > > >
 > > > So, we output the message to the system log when the filesystem is
 > > > remounted/unmounted.
 > > >
 > > > Signed-off-by: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>
 >
 > The question of whether this should be at the VFS layer is still an
 > open one, I think.  It is true that ext3 and ext4 does print some
I am recognizing it. But I think I have already explained its answer as follows:
  - A print mechanism has already been included at mount time.
  - The umount operation is opposite "mount operation". Therefore I think
    it is no problem that we add the print mechanism at the umount time.

 > filesystem specific information, but that could be handled via a new
 > method function in struct super_ops:
 >
 >        mount_msg(struct super *sb, char *buf, int buflen)
 >
However, I have noticed that the purpose of ext3/ext4 messages at mount time
is for specific information but not for a general purpose by this comment.

So, I think I should rearrange this feature into the VFS layer.
I try to reimplement it later.

Thanks,
Toshiyuki Okajima

Re: [PATCH 3/3][RFC](Repost) ext4: add a message in remount/umount for ext4

[Theodore Tso]

On Thu, Oct 01, 2009 at 12:20:17PM +0900, Toshiyuki Okajima wrote:
> I am recognizing it. But I think I have already explained its answer as follows:
>  - A print mechanism has already been included at mount time.

It's true that some file systems already are printing a message at
mount time; but when we abstract up something to the VFS layer, that's
also an opportunity to remove some kernel printk's from some
filesystems, including ext2/3/4 at the same time this feature is
introduced.

> > filesystem specific information, but that could be handled via a new
> > method function in struct super_ops:
> >
> >        mount_msg(struct super *sb, char *buf, int buflen)
> >

Note that what I was assuming is that we would is something like this
in the VFS mount code:

     printk(KERN_INFO "Device %s mounted file system type %s read-%s%s\n",
            sb->s_sid, sb->s_type->name, 
	    sb->s_flags & MS_RDONLY ? "only" : "write",
	    sb->s_op->mount_msg ? sb->s_op->mount_msg(sb) : "");

The advantage of this is that we would now have a single consistent
kernel message for all file systems, with some room for file system
specific message.

						- Ted

Re: [PATCH 3/3][RFC](Repost) ext4: add a message in remount/umount for ext4

[Toshiyuki Okajima]

Hi Ted,
thank you for your comment.

Theodore Tso wrote:
> On Thu, Oct 01, 2009 at 12:20:17PM +0900, Toshiyuki Okajima wrote:
>> I am recognizing it. But I think I have already explained its answer as follows:
>>  - A print mechanism has already been included at mount time.
> 
> It's true that some file systems already are printing a message at
> mount time; but when we abstract up something to the VFS layer, that's
> also an opportunity to remove some kernel printk's from some
> filesystems, including ext2/3/4 at the same time this feature is
> introduced.
> 
>>> filesystem specific information, but that could be handled via a new
>>> method function in struct super_ops:
>>>
>>>        mount_msg(struct super *sb, char *buf, int buflen)
>>>
> 
> Note that what I was assuming is that we would is something like this
> in the VFS mount code:
> 
>      printk(KERN_INFO "Device %s mounted file system type %s read-%s%s\n",
>             sb->s_sid, sb->s_type->name, 
> 	    sb->s_flags & MS_RDONLY ? "only" : "write",
> 	    sb->s_op->mount_msg ? sb->s_op->mount_msg(sb) : "");
> 
> The advantage of this is that we would now have a single consistent
> kernel message for all file systems, with some room for file system
> specific message.
OK.

I try to implement the message mechanism at mount/umount time like
your description ASAP.

Best Regards,
Toshiyuki Okajima