linux-ext4 - Re: [PATCH 5/7] add llseek

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Date:   Thu, 27 Jul 2023 20:26:47 +0800
From:   Hao Xu <hao.xu@...ux.dev>
To:     Dave Chinner <david@...morbit.com>
Cc:     io-uring@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Pavel Begunkov <asml.silence@...il.com>,
        Christian Brauner <brauner@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Stefan Roesch <shr@...com>, Clay Harris <bugs@...ycon.org>,
        "Darrick J . Wong" <djwong@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, Wanpeng Li <wanpengli@...cent.com>
Subject: Re: [PATCH 5/7] add llseek_nowait support for xfs

On 7/27/23 06:14, Dave Chinner wrote:
> On Wed, Jul 26, 2023 at 06:26:01PM +0800, Hao Xu wrote:
>> From: Hao Xu <howeyxu@...cent.com>
>>
>> Add llseek_nowait() operation for xfs, it acts just like llseek(). The
>> thing different is it delivers nowait parameter to iomap layer.
>>
>> Signed-off-by: Hao Xu <howeyxu@...cent.com>
>> ---
>>   fs/xfs/xfs_file.c | 29 +++++++++++++++++++++++++++--
>>   1 file changed, 27 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
>> index 73adc0aee2ff..cba82264221d 100644
>> --- a/fs/xfs/xfs_file.c
>> +++ b/fs/xfs/xfs_file.c
>> @@ -1257,10 +1257,11 @@ xfs_file_readdir(
>>   }
>>   
>>   STATIC loff_t
>> -xfs_file_llseek(
>> +__xfs_file_llseek(
>>   	struct file	*file,
>>   	loff_t		offset,
>> -	int		whence)
>> +	int		whence,
>> +	bool		nowait)
>>   {
>>   	struct inode		*inode = file->f_mapping->host;
>>   
>> @@ -1282,6 +1283,28 @@ xfs_file_llseek(
>>   	return vfs_setpos(file, offset, inode->i_sb->s_maxbytes);
>>   }
>>   
>> +STATIC loff_t
>> +xfs_file_llseek(
>> +	struct file	*file,
>> +	loff_t		offset,
>> +	int		whence)
>> +{
>> +	return __xfs_file_llseek(file, offset, whence, false);
>> +}
>> +
>> +STATIC loff_t
>> +xfs_file_llseek_nowait(
>> +	struct file	*file,
>> +	loff_t		offset,
>> +	int		whence,
>> +	bool		nowait)
>> +{
>> +	if (file->f_op == &xfs_file_operations)
>> +		return __xfs_file_llseek(file, offset, whence, nowait);
>> +	else
>> +		return generic_file_llseek(file, offset, whence);
>> +}
>> +
>>   #ifdef CONFIG_FS_DAX
>>   static inline vm_fault_t
>>   xfs_dax_fault(
>> @@ -1442,6 +1465,7 @@ xfs_file_mmap(
>>   
>>   const struct file_operations xfs_file_operations = {
>>   	.llseek		= xfs_file_llseek,
>> +	.llseek_nowait	= xfs_file_llseek_nowait,
>>   	.read_iter	= xfs_file_read_iter,
>>   	.write_iter	= xfs_file_write_iter,
>>   	.splice_read	= xfs_file_splice_read,
>> @@ -1467,6 +1491,7 @@ const struct file_operations xfs_dir_file_operations = {
>>   	.read		= generic_read_dir,
>>   	.iterate_shared	= xfs_file_readdir,
>>   	.llseek		= generic_file_llseek,
>> +	.llseek_nowait	= xfs_file_llseek_nowait,
>>   	.unlocked_ioctl	= xfs_file_ioctl,
>>   #ifdef CONFIG_COMPAT
>>   	.compat_ioctl	= xfs_file_compat_ioctl,
> 
> This is pretty nasty. It would be far better just to change the
> .llseek method than to inflict this on every filesystem for the
> forseeable future.
> 
> Not that I'm a fan of passing "nowait" booleans all through the file
> operations methods - that way lies madness. We use a control
> structure for the IO path operations (kiocb) to hold per-call
> context information, perhaps we need something similar for these
> other methods that people are wanting to hook up to io_uring (e.g.
> readdir) so taht we don't have to play whack-a-mole with every new
> io_uring method that people want and then end up with a different
> nowait solution for every method.
> 
> -Dave.

whack-a-mole is exactly what I thought when I tried to find a place to
hold that...I'll think about it in next version, a generic structure for
io_uring is good I believe. I'll update this patchset after the getdents
stuff are merged.

Thanks,
Hao