Re: [PATCH v20 05/12] fs/read_write: Enable copy_file_range for block device.

[Dave Chinner]

On Mon, May 20, 2024 at 03:50:18PM +0530, Nitesh Shetty wrote:
> From: Anuj Gupta <anuj20.g@xxxxxxxxxxx>
> 
> This is a prep patch. Allow copy_file_range to work for block devices.
> Relaxing generic_copy_file_checks allows us to reuse the existing infra,
> instead of adding a new user interface for block copy offload.
> Change generic_copy_file_checks to use ->f_mapping->host for both inode_in
> and inode_out. Allow block device in generic_file_rw_checks.
> 
> Reviewed-by: Hannes Reinecke <hare@xxxxxxx>
> Signed-off-by: Anuj Gupta <anuj20.g@xxxxxxxxxxx>
> Signed-off-by: Nitesh Shetty <nj.shetty@xxxxxxxxxxx>
> ---
>  fs/read_write.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/read_write.c b/fs/read_write.c
> index ef6339391351..31645ca5ed58 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -1413,8 +1413,8 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in,
>  				    struct file *file_out, loff_t pos_out,
>  				    size_t *req_count, unsigned int flags)
>  {
> -	struct inode *inode_in = file_inode(file_in);
> -	struct inode *inode_out = file_inode(file_out);
> +	struct inode *inode_in = file_in->f_mapping->host;
> +	struct inode *inode_out = file_out->f_mapping->host;
>  	uint64_t count = *req_count;
>  	loff_t size_in;
>  	int ret;

Ok, so this changes from file->f_inode to file->mapping->host. No
doubt this is because of how bdev inode mappings are munged.
However, the first code that is run here is:

	ret = generic_file_rw_checks(file_in, file_out);

and that function still uses file_inode().

Hence there checks:

> @@ -1726,7 +1726,9 @@ int generic_file_rw_checks(struct file *file_in, struct file *file_out)
>  	/* Don't copy dirs, pipes, sockets... */
>  	if (S_ISDIR(inode_in->i_mode) || S_ISDIR(inode_out->i_mode))
>  		return -EISDIR;
> -	if (!S_ISREG(inode_in->i_mode) || !S_ISREG(inode_out->i_mode))
> +	if (!S_ISREG(inode_in->i_mode) && !S_ISBLK(inode_in->i_mode))
> +		return -EINVAL;
> +	if ((inode_in->i_mode & S_IFMT) != (inode_out->i_mode & S_IFMT))
>  		return -EINVAL;

... are being done on different inodes to the rest of
generic_copy_file_checks() when block devices are used.

Is this correct? If so, this needs a pair of comments (one for each
function) to explain why the specific inode used for these functions
is correct for block devices....

-Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx