Re: [PATCH 08/15] btrfs: Introduce btrfs_write_check()

[Josef Bacik <josef@toxicpanda.com>]

On 9/21/20 10:43 AM, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> 
> btrfs_write_check() checks for all parameters in one place before
> beginning a write. This does away with inode_unlock() after every check.
> In the later patches, it will help push inode_lock/unlock() in buffered
> and direct write functions respectively.
> 
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> ---
>   fs/btrfs/file.c | 159 ++++++++++++++++++++++++------------------------
>   1 file changed, 81 insertions(+), 78 deletions(-)
> 
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index ca374cb5ffc9..0f961ce1fa98 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1615,6 +1615,85 @@ void btrfs_check_nocow_unlock(struct btrfs_inode *inode)
>   	btrfs_drew_write_unlock(&inode->root->snapshot_lock);
>   }
>   
> +static void update_time_for_write(struct inode *inode)
> +{
> +	struct timespec64 now;
> +
> +	if (IS_NOCMTIME(inode))
> +		return;
> +
> +	now = current_time(inode);
> +	if (!timespec64_equal(&inode->i_mtime, &now))
> +		inode->i_mtime = now;
> +
> +	if (!timespec64_equal(&inode->i_ctime, &now))
> +		inode->i_ctime = now;
> +
> +	if (IS_I_VERSION(inode))
> +		inode_inc_iversion(inode);
> +}
> +
> +static size_t btrfs_write_check(struct kiocb *iocb, struct iov_iter *from)
> +{
> +	struct file *file = iocb->ki_filp;
> +	struct inode *inode = file_inode(file);
> +	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> +	loff_t pos = iocb->ki_pos;
> +	size_t count = iov_iter_count(from);
> +	int err;
> +	loff_t oldsize;
> +	loff_t start_pos;
> +
> +	err = generic_write_checks(iocb, from);
> +	if (err <= 0)
> +		return err;
> +
> +	if (iocb->ki_flags & IOCB_NOWAIT) {
> +		size_t nocow_bytes = count;
> +
> +		/*
> +		 * We will allocate space in case nodatacow is not set,
> +		 * so bail
> +		 */
> +		if (check_nocow_nolock(BTRFS_I(inode), pos, &nocow_bytes)
> +		    <= 0)
> +			return -EAGAIN;
> +		/*
> +		 * There are holes in the range or parts of the range that must
> +		 * be COWed (shared extents, RO block groups, etc), so just bail
> +		 * out.
> +		 */
> +		if (nocow_bytes < count)
> +			return -EAGAIN;
> +	}
> +
> +	current->backing_dev_info = inode_to_bdi(inode);
> +	err = file_remove_privs(file);
> +	if (err)
> +		return err;
> +
> +	/*
> +	 * We reserve space for updating the inode when we reserve space for the
> +	 * extent we are going to write, so we will enospc out there.  We don't
> +	 * need to start yet another transaction to update the inode as we will
> +	 * update the inode when we finish writing whatever data we write.
> +	 */
> +	update_time_for_write(inode);
> +
> +	start_pos = round_down(pos, fs_info->sectorsize);
> +	oldsize = i_size_read(inode);
> +	if (start_pos > oldsize) {
> +		/* Expand hole size to cover write data, preventing empty gap */
> +		loff_t end_pos = round_up(pos + count,
> +					  fs_info->sectorsize);
> +		err = btrfs_cont_expand(inode, oldsize, end_pos);
> +		if (err)
> +			return err;

In this case we're not re-setting current->backing_dev_info to NULL.  Thanks,

Josef