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

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Message-ID: <7ttdwk46hkj6ohdyq3ruwb2zkskzrpicz7dpf4g53v32nh7mgy@5g63yuoyotyi>
Date: Mon, 5 Feb 2024 16:20:32 +0100
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: John Garry <john.g.garry@...cle.com>
Cc: hch@....de, 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, 
	p.raghav@...sung.com
Subject: Re: [PATCH 1/6] fs: iomap: Atomic write support

On Wed, Jan 24, 2024 at 02:26:40PM +0000, John Garry wrote:
> Add flag IOMAP_ATOMIC_WRITE to indicate to the FS that an atomic write
> bio is being created and all the rules there need to be followed.
> 
> It is the task of the FS iomap iter callbacks to ensure that the mapping
> created adheres to those rules, like size is power-of-2, is at a
> naturally-aligned offset, etc. However, checking for a single iovec, i.e.
> iter type is ubuf, is done in __iomap_dio_rw().
> 
> A write should only produce a single bio, so error when it doesn't.
> 
> Signed-off-by: John Garry <john.g.garry@...cle.com>
> ---
>  fs/iomap/direct-io.c  | 21 ++++++++++++++++++++-
>  fs/iomap/trace.h      |  3 ++-
>  include/linux/iomap.h |  1 +
>  3 files changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index bcd3f8cf5ea4..25736d01b857 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -275,10 +275,12 @@ static inline blk_opf_t iomap_dio_bio_opflags(struct iomap_dio *dio,
>  static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
>  		struct iomap_dio *dio)
>  {
> +	bool atomic_write = iter->flags & IOMAP_ATOMIC;

Minor nit: the commit says IOMAP_ATOMIC_WRITE and you set the enum as
IOMAP_ATOMIC in the code.

As the atomic semantics only apply to write, the commit could be just
reworded to reflect the code?

<snip>
> diff --git a/fs/iomap/trace.h b/fs/iomap/trace.h
> index c16fd55f5595..c95576420bca 100644
> --- a/fs/iomap/trace.h
> +++ b/fs/iomap/trace.h
> @@ -98,7 +98,8 @@ DEFINE_RANGE_EVENT(iomap_dio_rw_queued);
>  	{ IOMAP_REPORT,		"REPORT" }, \
>  	{ IOMAP_FAULT,		"FAULT" }, \
>  	{ IOMAP_DIRECT,		"DIRECT" }, \
> -	{ IOMAP_NOWAIT,		"NOWAIT" }
> +	{ IOMAP_NOWAIT,		"NOWAIT" }, \
> +	{ IOMAP_ATOMIC,		"ATOMIC" }
>