Re: [RFC PATCH] ext4: Fix fallocate to update the file size in each transaction.

[Eric Sandeen <sandeen@redhat.com>]

Aneesh Kumar K.V wrote:
> ext4_fallocate need to update file size in each transaction. Otherwise
> ife we crash the file size won't be updated. We were also not marking
> the inode dirty after updating file size before. 

This led to losing the size update when unmounted...

> Also when we try to
> retry allocation due to ENOSPC make sure we reset the variable ret so
> that we actually do a retry.

That's a few alsos.  Should this be more than one patch when committed?

-Eric

> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> ---
>  fs/ext4/extents.c |   78 +++++++++++++++++++++--------------------------------
>  1 files changed, 31 insertions(+), 47 deletions(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index dcdf92a..09dd3c5 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -2783,6 +2783,26 @@ int ext4_ext_writepage_trans_blocks(struct inode *inode, int num)
>  	return needed;
>  }
>  
> +static void ext4_falloc_update_inode(struct inode *inode,
> +					int mode, loff_t new_size)
> +{
> +	struct timespec now;
> +
> +	now = current_fs_time(inode->i_sb);
> +	if (!timespec_equal(&inode->i_ctime, &now))
> +		inode->i_ctime = now;

This used to depend on blocks actually being allocated; it looks like it
doesn't anymore?

> +	/*
> +	 * Update only when preallocation was requested beyond
> +	 * the file size.
> +	 */
> +	if (!(mode & FALLOC_FL_KEEP_SIZE) &&
> +				new_size > i_size_read(inode)) {
> +		i_size_write(inode, new_size);
> +		EXT4_I(inode)->i_disksize = i_size_read(inode);
> +	}
> +
> +}

Ok, I think this is all cleaner...

>  /*
>   * preallocate space for a file. This implements ext4's fallocate inode
>   * operation, which gets called from sys_fallocate system call.
> @@ -2794,8 +2814,8 @@ long ext4_fallocate(struct inode *inode, int mode, loff_t offset, loff_t len)
>  {
>  	handle_t *handle;
>  	ext4_lblk_t block;
> +	loff_t new_size;
>  	unsigned long max_blocks;
> -	ext4_fsblk_t nblocks = 0;
>  	int ret = 0;
>  	int ret2 = 0;
>  	int retries = 0;
> @@ -2814,8 +2834,7 @@ long ext4_fallocate(struct inode *inode, int mode, loff_t offset, loff_t len)
>  		return -ENODEV;
>  
>  	block = offset >> blkbits;
> -	max_blocks = (EXT4_BLOCK_ALIGN(len + offset, blkbits) >> blkbits)
> -			- block;
> +	max_blocks = EXT4_BLOCK_ALIGN(len, blkbits) >> blkbits;

Ok, this makes much more sense IMHO.

>  
>  	/*
>  	 * credits to insert 1 extent into extent tree + buffers to be able to
> @@ -2848,28 +2867,13 @@ retry:
>  			ret2 = ext4_journal_stop(handle);
>  			break;
>  		}
> -		if (ret > 0) {
> -			/* check wrap through sign-bit/zero here */
> -			if ((block + ret) < 0 || (block + ret) < block) {
> -				ret = -EIO;
> -				ext4_mark_inode_dirty(handle, inode);
> -				ret2 = ext4_journal_stop(handle);
> -				break;
> -			}
> -			if (buffer_new(&map_bh) && ((block + ret) >
> -			    (EXT4_BLOCK_ALIGN(i_size_read(inode), blkbits)
> -			    >> blkbits)))
> -					nblocks = nblocks + ret;
> -		}
> +		if ((block + ret) >= (EXT4_BLOCK_ALIGN(offset + len,
> +						blkbits) >> blkbits))
> +			new_size = offset + len;
> +		else
> +			new_size = (block + ret) << blkbits;

Since we called ext4_get_blocks_wrap with max_blocks, will we really end
up with more blocks allocated than we asked for?  And do we no longer
need the wrap checks?  (I'd expect that to be tested higher up with the
original offset+len requested, no?)

> -		/* Update ctime if new blocks get allocated */
> -		if (nblocks) {
> -			struct timespec now;
> -
> -			now = current_fs_time(inode->i_sb);
> -			if (!timespec_equal(&inode->i_ctime, &now))
> -				inode->i_ctime = now;
> -		}
> +		ext4_falloc_update_inode(inode, mode, new_size);
>  
>  		ext4_mark_inode_dirty(handle, inode);
>  		ret2 = ext4_journal_stop(handle);
> @@ -2877,30 +2881,10 @@ retry:
>  			break;
>  	}
>  
> -	if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
> +	if (ret == -ENOSPC &&
> +			ext4_should_retry_alloc(inode->i_sb, &retries)) {
> +		ret = 0;
>  		goto retry;
> -
> -	/*
> -	 * Time to update the file size.
> -	 * Update only when preallocation was requested beyond the file size.
> -	 */
> -	if (!(mode & FALLOC_FL_KEEP_SIZE) &&
> -	    (offset + len) > i_size_read(inode)) {
> -		if (ret > 0) {
> -			/*
> -			 * if no error, we assume preallocation succeeded
> -			 * completely
> -			 */
> -			i_size_write(inode, offset + len);
> -			EXT4_I(inode)->i_disksize = i_size_read(inode);
> -		} else if (ret < 0 && nblocks) {
> -			/* Handle partial allocation scenario */
> -			loff_t newsize;
> -
> -			newsize  = (nblocks << blkbits) + i_size_read(inode);
> -			i_size_write(inode, EXT4_BLOCK_ALIGN(newsize, blkbits));
> -			EXT4_I(inode)->i_disksize = i_size_read(inode);
> -		}
>  	}
>  
>  	mutex_unlock(&inode->i_mutex);