linux-ext4 - Re: [PATCH RESEND] ext4: make sure O_(D)SYNC semantic in ext4

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Message-ID: <20120614001531.GB22646@thunk.org>
Date:	Wed, 13 Jun 2012 20:15:31 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Zheng Liu <gnehzuil.liu@...il.com>
Cc:	linux-ext4@...r.kernel.org, Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [PATCH RESEND] ext4: make sure O_(D)SYNC semantic in
 ext4_fallocate()

Hi Zheng,

I finally got around to reviewing this patch and I had one comment

> Ext4 must make sure the transaction to be commited to the disk when
> user opens a file with O_(D)SYNC flag and do a fallocate(2) call.
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 74f23c2..00e32d9 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -4356,6 +4356,8 @@ retry:
>  			ret = PTR_ERR(handle);
>  			break;
>  		}
> +		if (file->f_flags & O_SYNC)
> +			ext4_handle_sync(handle);
>  		ret = ext4_map_blocks(handle, inode, &map, flags);
>  		if (ret <= 0) {
>  #ifdef EXT4FS_DEBUG

For a large fallocate(), it can require multiple calls to
ext4_map_blocks(), and we should only sync after we've allocated the
last segment.  We should also not force a sync if there is an error
allocating blocks.  So it seems to me this patch would be better; what
do you think?

						- Ted

commit b790d70be9515dfaba59b0be0aff373e6867826d
Author: Zheng Liu <gnehzuil.liu@...il.com>
Date:   Wed Jun 13 20:15:01 2012 -0400

    ext4: honor O_(D)SYNC semantic in ext4_fallocate()
    
    Ext4 must make sure the transaction to be commited to the disk when
    user opens a file with O_(D)SYNC flag and do a fallocate(2) call.
    
    This problem had been reported by Christoph Hellwig in this thread:
    http://www.spinics.net/lists/linux-btrfs/msg13621.html
    
    Reported-by: Christoph Hellwig <hch@...radead.org>
    Signed-off-by: Zheng Liu <wenqing.lz@...bao.com>
    Signed-off-by: "Theodore Ts'o" <tytso@....edu>

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 91341ec..f1089cb 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4420,6 +4420,8 @@ retry:
 		ext4_falloc_update_inode(inode, mode, new_size,
 					 (map.m_flags & EXT4_MAP_NEW));
 		ext4_mark_inode_dirty(handle, inode);
+		if ((file->f_flags & O_SYNC) && ret >= max_blocks)
+			ext4_handle_sync(handle);
 		ret2 = ext4_journal_stop(handle);
 		if (ret2)
 			break;
--
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