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Date:   Mon, 24 Jul 2023 11:16:06 +0530
From:   Nitesh Shetty <nj.shetty@samsung.com>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Jens Axboe <axboe@kernel.dk>, Jonathan Corbet <corbet@lwn.net>,
        Alasdair Kergon <agk@redhat.com>,
        Mike Snitzer <snitzer@kernel.org>, dm-devel@redhat.com,
        Keith Busch <kbusch@kernel.org>,
        Sagi Grimberg <sagi@grimberg.me>,
        Chaitanya Kulkarni <kch@nvidia.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        martin.petersen@oracle.com, linux-scsi@vger.kernel.org,
        willy@infradead.org, hare@suse.de, djwong@kernel.org,
        bvanassche@acm.org, ming.lei@redhat.com, dlemoal@kernel.org,
        nitheshshetty@gmail.com, gost.dev@samsung.com,
        Anuj Gupta <anuj20.g@samsung.com>, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v13 4/9] fs, block: copy_file_range for def_blk_ops for
 direct block device
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On 23/07/20 09:57AM, Christoph Hellwig wrote:
>> +/* Copy source offset from source block device to destination block
>> + * device. Returns the length of bytes copied.
>> + */
>> +ssize_t blkdev_copy_offload_failfast(
>> +		struct block_device *bdev_in, loff_t pos_in,
>> +		struct block_device *bdev_out, loff_t pos_out,
>> +		size_t len, gfp_t gfp_mask)
>
>This is an odd and very misnamed interface.
>
>Either we have a klkdev_copy() interface that automatically falls back
>to a fallback (maybe with an opt-out), or we have separate
>blkdev_copy_offload/blkdev_copy_emulated interface and let the caller
>decide.  But none of that really is "failfast".
>
>Also this needs to go into the helpers patch and not a patch that is
>supposed to just wire copying up for block device node.
>
Acked.

>> index b07de77ef126..d27148a2543f 100644
>> --- a/fs/read_write.c
>> +++ b/fs/read_write.c
>> @@ -1447,7 +1447,8 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in,
>>  		return -EOVERFLOW;
>>
>>  	/* Shorten the copy to EOF */
>> -	size_in = i_size_read(inode_in);
>> +	size_in = i_size_read(file_in->f_mapping->host);
>
>generic_copy_file_checks needs to be fixed to use ->mapping->host both
>or inode_in and inode_out at the top of the file instead of this
>band aid.  And that needs to be a separate patch with a Fixes tag.
>
Addressed below.

>> @@ -1708,7 +1709,9 @@ 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_ISREG(inode_out->i_mode)) &&
>> +		(!S_ISBLK(inode_in->i_mode) || !S_ISBLK(inode_out->i_mode)))
>
>This is using weird indentation, and might also not be doing
>exactly what we want.  I think the better thing to do here is to:
>
> 1) check for the accetable types only on the in inode
> 2) have a check that the mode matches for the in and out inodes
>
>And please do this as a separate prep patch instead of hiding it here.
>
Agreed. We will send a separate patch, that enables copy_file_range on
block devices.

Thank you,
Nitesh Shetty

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