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

[Nitesh Shetty]

On 26/05/24 09:02AM, Dave Chinner wrote:
> 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....
We were getting wrong size with file_inode() for block device, but we
missed to do it here in generic_file_rw_checks.
We will change the generic_file_rw_checks to use file->mapping->host
to make it consistent.

Thank You,
Nitesh Shetty