From: Kanchan Joshi <[email protected]>
To: Christoph Hellwig <[email protected]>
Cc: [email protected], [email protected], [email protected],
[email protected], [email protected],
[email protected], [email protected],
[email protected], [email protected],
[email protected], [email protected],
[email protected], [email protected],
[email protected], Arnav Dawn <[email protected]>
Subject: Re: [PATCH v2 1/2] fs,block: Introduce RWF_ZONE_APPEND and handling in direct IO path
Date: Sat, 27 Jun 2020 02:45:14 +0530 [thread overview]
Message-ID: <20200626211514.GA24762@test-zns> (raw)
In-Reply-To: <[email protected]>
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On Fri, Jun 26, 2020 at 09:58:46AM +0100, Christoph Hellwig wrote:
>To restate my previous NAK:
>
>A low-level protocol detail like RWF_ZONE_APPEND has absolutely no
>business being exposed in the Linux file system interface.
>
>And as mentioned before I think the idea of returning the actual
>position written for O_APPEND writes totally makes sense, and actually
>is generalizable to all files. Together with zonefs that gives you a
>perfect interface for zone append.
>
>On Thu, Jun 25, 2020 at 10:45:48PM +0530, Kanchan Joshi wrote:
>> Introduce RWF_ZONE_APPEND flag to represent zone-append.
>
>And no one but us select few even know what zone append is, nevermind
>what the detailed semantics are. If you add a userspace API you need
>to very clearly document the semantics inluding errors and corner cases.
For block IO path (which is the scope of this patchset) there is no
probelm in using RWF_APPEND for zone-append, because it does not do
anything for block device. We can use that, avoiding introduction of
RWF_ZONE_APPEND in user-space.
In kernel, will it be fine to keep IOCB_ZONE_APPEND apart from
IOCB_APPEND? Reason being, this can help to isolate the code meant only
for zone-append from the one that is already present for conventional
append.
Snippet from quick reference -
static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
if (flags & RWF_APPEND)
ki->ki_flags |= IOCB_APPEND;
+ if (flags & RWF_ZONE_APPEND) {
+ /* currently support block device only */
+ umode_t mode = file_inode(ki->ki_filp)->i_mode;
+
+ if (!(S_ISBLK(mode)))
+ return -EOPNOTSUPP;
+ ki->ki_flags |= IOCB_ZONE_APPEND;
+ }
As for file I/O in future, I see a potential problem with RWF_APPEND.
In io_uring, zone-append requires bit of pre/post processing, which
ideally should be done only for zone-append case. A ZoneFS file using
RWF_APPEND as a mean to invoke zone-append vs a regular file (hosted on
some other FS) requiring conventional RWF_APPEND - both will execute
that processing.
Is there a good way to differentiate ZoneFS file from another file which
only wants use conventional file-append?
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next prev parent reply other threads:[~2020-06-26 21:18 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20200625171829epcas5p268486a0780571edb4999fc7b3caab602@epcas5p2.samsung.com>
2020-06-25 17:15 ` [PATCH v2 0/2] zone-append support in io-uring and aio Kanchan Joshi
[not found] ` <CGME20200625171834epcas5p226a24dfcb84cfa83fe29a2bd17795d85@epcas5p2.samsung.com>
2020-06-25 17:15 ` [PATCH v2 1/2] fs,block: Introduce RWF_ZONE_APPEND and handling in direct IO path Kanchan Joshi
2020-06-26 2:50 ` Damien Le Moal
2020-06-29 18:32 ` Kanchan Joshi
2020-06-30 0:37 ` Damien Le Moal
2020-06-30 7:40 ` Kanchan Joshi
2020-06-30 7:52 ` Damien Le Moal
2020-06-30 7:56 ` Damien Le Moal
2020-06-30 8:16 ` Kanchan Joshi
2020-06-26 8:58 ` Christoph Hellwig
2020-06-26 21:15 ` Kanchan Joshi [this message]
2020-06-27 6:51 ` Christoph Hellwig
[not found] ` <CGME20200625171838epcas5p449183e12770187142d8d55a9bf422a8d@epcas5p4.samsung.com>
2020-06-25 17:15 ` [PATCH v2 2/2] io_uring: add support for zone-append Kanchan Joshi
2020-06-25 19:40 ` Pavel Begunkov
2020-06-26 3:11 ` [PATCH v2 0/2] zone-append support in io-uring and aio Damien Le Moal
2020-06-26 6:37 ` javier.gonz
2020-06-26 6:56 ` Damien Le Moal
2020-06-26 7:03 ` [email protected]
2020-06-26 22:15 ` Kanchan Joshi
2020-06-30 12:46 ` Matthew Wilcox
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