Re: [PATCH v5 8/9] btrfs: implement RWF_ENCODED reads

[Josef Bacik <josef@toxicpanda.com>]

On 8/21/20 3:38 AM, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
> 
> There are 4 main cases:
> 
> 1. Inline extents: we copy the data straight out of the extent buffer.
> 2. Hole/preallocated extents: we fill in zeroes.
> 3. Regular, uncompressed extents: we read the sectors we need directly
>     from disk.
> 4. Regular, compressed extents: we read the entire compressed extent
>     from disk and indicate what subset of the decompressed extent is in
>     the file.
> 
> This initial implementation simplifies a few things that can be improved
> in the future:
> 
> - We hold the inode lock during the operation.
> - Cases 1, 3, and 4 allocate temporary memory to read into before
>    copying out to userspace.
> 
> Signed-off-by: Omar Sandoval <osandov@fb.com>


<snip>

> +	tmp = kmalloc(count, GFP_NOFS);
> +	if (!tmp) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +	read_extent_buffer(leaf, tmp, ptr, count);
> +	btrfs_free_path(path);

Why not just btrfs_release_path(), you're freeing below anyway.

Also a mention that we're explicitly not handling read repairs and backup copies 
would be good in the changelog as well.  Thanks,

Josef