linux-kernel - Re: [PATCH 1/6] fs: iomap: Atomic write support

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Date: Thu, 15 Feb 2024 11:08:40 +0000
From: John Garry <john.g.garry@...cle.com>
To: Christoph Hellwig <hch@....de>
Cc: "Darrick J. Wong" <djwong@...nel.org>, viro@...iv.linux.org.uk,
        brauner@...nel.org, dchinner@...hat.com, jack@...e.cz,
        chandan.babu@...cle.com, martin.petersen@...cle.com,
        linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
        ojaswin@...ux.ibm.com
Subject: Re: [PATCH 1/6] fs: iomap: Atomic write support

On 13/02/2024 08:20, John Garry wrote:
> On 13/02/2024 06:55, Christoph Hellwig wrote:
>> On Mon, Feb 05, 2024 at 11:29:57AM +0000, John Garry wrote:
>>>> Also, what's the meaning of REQ_OP_READ | REQ_ATOMIC?
>>> REQ_ATOMIC will be ignored for REQ_OP_READ. I'm following the same 
>>> policy
>>> as something like RWF_SYNC for a read.
>> We've been rather sloppy with these flags in the past, which isn't
>> a good thing.  Let's add proper checking for new interfaces.

How about something like this:

----8<----

-static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
+static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags, int 
type)
  {
   int kiocb_flags = 0;

..

+ if (flags & RWF_ATOMIC) {
+ 	if (type == READ)
+ 		return -EOPNOTSUPP;
+ 	if (!(ki->ki_filp->f_mode & FMODE_CAN_ATOMIC_WRITE))
+ 		return -EOPNOTSUPP;
+ }
   kiocb_flags |= (__force int) (flags & RWF_SUPPORTED);
   if (flags & RWF_SYNC)
  	 kiocb_flags |= IOCB_DSYNC;

---->8----

I don't see a better place to add this check.

John