linux-kernel - Re: [PATCH v20 05/12] fs/read_write: Enable copy_file

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Date: Tue, 28 May 2024 05:57:33 +0000
From: Nitesh Shetty <nj.shetty@...sung.com>
To: Dave Chinner <david@...morbit.com>
Cc: Jens Axboe <axboe@...nel.dk>, Jonathan Corbet <corbet@....net>, Alasdair
	Kergon <agk@...hat.com>, Mike Snitzer <snitzer@...nel.org>, Mikulas Patocka
	<mpatocka@...hat.com>, Keith Busch <kbusch@...nel.org>, Christoph Hellwig
	<hch@....de>, Sagi Grimberg <sagi@...mberg.me>, Chaitanya Kulkarni
	<kch@...dia.com>, Alexander Viro <viro@...iv.linux.org.uk>, Christian
	Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	martin.petersen@...cle.com, bvanassche@....org, hare@...e.de,
	damien.lemoal@...nsource.wdc.com, anuj20.g@...sung.com, joshi.k@...sung.com,
	nitheshshetty@...il.com, gost.dev@...sung.com, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	dm-devel@...ts.linux.dev, linux-nvme@...ts.infradead.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v20 05/12] fs/read_write: Enable copy_file_range for
 block device.

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@...sung.com>
>>
>> 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@...e.de>
>> Signed-off-by: Anuj Gupta <anuj20.g@...sung.com>
>> Signed-off-by: Nitesh Shetty <nj.shetty@...sung.com>
>> ---
>>  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