On Sun 16-04-23 15:38:37, Ritesh Harjani (IBM) wrote:
> Some of the higher layers like iomap takes inode_lock() when calling
> generic_write_sync().
> Also writeback already happens from other paths without inode lock,
> so it's difficult to say that we really need sync_mapping_buffers() to
> take any inode locking here. Having said that, let's add
> generic_buffer_fsync() implementation in buffer.c with no
> inode_lock/unlock() for now so that filesystems like ext2 and
> ext4's nojournal mode can use it.
>
> Ext4 when got converted to iomap for direct-io already copied it's own
> variant of __generic_file_fsync() without lock. Hence let's add a helper
> API and use it both in ext2 and ext4.
>
> Later we can review other filesystems as well to see if we can make
> generic_buffer_fsync() which does not take any inode_lock() as the
> default path.
>
> Tested-by: Disha Goel <disgoel@xxxxxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
There is a problem with generic_buffer_fsync() that it does not call
blkdev_issue_flush() so the caller is responsible for doing that. That's
necessary for ext2 & ext4 so fine for now. But historically this was the
case with generic_file_fsync() as well and that led to many filesystem
forgetting to flush caches from fsync(2). What is our transition plan for
these filesystems that currently do the cache flush from
generic_file_fsync()? Do we want to eventually keep generic_file_fsync()
doing the cache flush and call generic_buffer_fsync() instead of
__generic_buffer_fsync() from it?
Honza
> ---
> fs/buffer.c | 43 +++++++++++++++++++++++++++++++++++++
> include/linux/buffer_head.h | 2 ++
> 2 files changed, 45 insertions(+)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 9e1e2add541e..df98f1966a71 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -593,6 +593,49 @@ int sync_mapping_buffers(struct address_space *mapping)
> }
> EXPORT_SYMBOL(sync_mapping_buffers);
>
> +/**
> + * generic_buffer_fsync - generic buffer fsync implementation
> + * for simple filesystems with no inode lock
> + *
> + * @file: file to synchronize
> + * @start: start offset in bytes
> + * @end: end offset in bytes (inclusive)
> + * @datasync: only synchronize essential metadata if true
> + *
> + * This is a generic implementation of the fsync method for simple
> + * filesystems which track all non-inode metadata in the buffers list
> + * hanging off the address_space structure.
> + */
> +int generic_buffer_fsync(struct file *file, loff_t start, loff_t end,
> + bool datasync)
> +{
> + struct inode *inode = file->f_mapping->host;
> + int err;
> + int ret;
> +
> + err = file_write_and_wait_range(file, start, end);
> + if (err)
> + return err;
> +
> + ret = sync_mapping_buffers(inode->i_mapping);
> + if (!(inode->i_state & I_DIRTY_ALL))
> + goto out;
> + if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
> + goto out;
> +
> + err = sync_inode_metadata(inode, 1);
> + if (ret == 0)
> + ret = err;
> +
> +out:
> + /* check and advance again to catch errors after syncing out buffers */
> + err = file_check_and_advance_wb_err(file);
> + if (ret == 0)
> + ret = err;
> + return ret;
> +}
> +EXPORT_SYMBOL(generic_buffer_fsync);
> +
> /*
> * Called when we've recently written block `bblock', and it is known that
> * `bblock' was for a buffer_boundary() buffer. This means that the block at
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index 8f14dca5fed7..3170d0792d52 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -211,6 +211,8 @@ int inode_has_buffers(struct inode *);
> void invalidate_inode_buffers(struct inode *);
> int remove_inode_buffers(struct inode *inode);
> int sync_mapping_buffers(struct address_space *mapping);
> +int generic_buffer_fsync(struct file *file, loff_t start, loff_t end,
> + bool datasync);
> void clean_bdev_aliases(struct block_device *bdev, sector_t block,
> sector_t len);
> static inline void clean_bdev_bh_alias(struct buffer_head *bh)
> --
> 2.39.2
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
