linux-ext4 - Re: [PATCH v10 0/5] add support for direct I/O with fscrypt using blk-crypto

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Date:   Mon, 24 Jan 2022 10:03:32 +1100
From:   Dave Chinner <david@...morbit.com>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     Eric Biggers <ebiggers@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        linux-fscrypt@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-xfs@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>
Subject: Re: [PATCH v10 0/5] add support for direct I/O with fscrypt using
 blk-crypto

On Thu, Jan 20, 2022 at 06:36:03PM -0800, Darrick J. Wong wrote:
> On Fri, Jan 21, 2022 at 10:57:55AM +1100, Dave Chinner wrote:
> Sure.  How's this?  I couldn't think of a real case of directio
> requiring different alignments for pos and bytecount, so the only real
> addition here is the alignment requirements for best performance.
> 
> struct statx {
> ...
> 	/* 0x90 */
> 	__u64	stx_mnt_id;
> 
> 	/* Memory buffer alignment required for directio, in bytes. */
> 	__u32	stx_dio_mem_align;

	__32	stx_mem_align_dio;

(for consistency with suggestions below)

> 
> 	/* File range alignment required for directio, in bytes. */
> 	__u32	stx_dio_fpos_align_min;

"fpos" is not really a user term - "offset" is the userspace term for
file position, and it's much less of a random letter salad if it's
named that way. Also, we don't need "min" in the name; the
description of the field in the man page can give all the gory
details about it being the minimum required alignment.

	__u32	stx_offset_align_dio;

> 
> 	/* 0xa0 */
> 
> 	/* File range alignment needed for best performance, in bytes. */
> 	__u32	stx_dio_fpos_align_opt;

This is a common property of both DIO and buffered IO, so no need
for it to be dio-only property.

	__u32	stx_offset_align_optimal;

> 
> 	/* Maximum size of a directio request, in bytes. */
> 	__u32	stx_dio_max_iosize;

Unnecessary, it will always be the syscall max IO size, because the
internal DIO code will slice and dice it down to the max sizes the
hardware supports.

> #define STATX_DIRECTIO	0x00001000U	/* Want/got directio geometry */
> 
> How about that?

Mostly seems reasonable at a first look.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com