All of lore.kernel.org
 help / color / mirror / Atom feed
From: "Martin K. Petersen" <martin.petersen@oracle.com>
To: Mike Snitzer <snitzer@redhat.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>,
	Christoph Hellwig <hch@infradead.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] block: warn if blk_stack_limits() undermines atomicity
Date: Tue, 23 Feb 2010 12:10:44 -0500	[thread overview]
Message-ID: <yq1635nop2j.fsf@sermon.lab.mkp.net> (raw)
In-Reply-To: <20100222204920.GA24514@redhat.com> (Mike Snitzer's message of "Mon, 22 Feb 2010 15:49:20 -0500")

>>>>> "Mike" == Mike Snitzer <snitzer@redhat.com> writes:

Mike> For instance, a 512 byte device and a 4K device may be combined
Mike> into a single logical DM device; the resulting DM device would
Mike> have a logical_block_size of 4K.  Filesystems layered on such a
Mike> hybrid device assume that 4K will be written atomically but in
Mike> reality that 4K will be split into 8 512 byte IOs when issued to
Mike> the 512 byte device.

Not really.  It'll be issued as one I/O with a smaller LBA count but an
identical data payload.


Mike> Using a 4K logical_block_size for the higher-level DM device
Mike> increases potential for a partial write to the 512b device if
Mike> there is a system crash.

That's a definite maybe :)


Mike> [NOTE: setting "misaligned" for this warning is somewhat awkward
Mike> but blk_stack_limits() return of -1 can be viewed as there was an
Mike> "alignment inconsistency".  Would it be better to return -1 but
Mike> avoid setting t->misaligned?]

I don't have a problem with printing a warning but I don't think this
qualifies as misalignment on the grounds that the error scenario is in
the hypothetical bucket and not a deterministic thing.

-- 
Martin K. Petersen	Oracle Linux Engineering

  reply	other threads:[~2010-02-23 17:11 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-02-22 20:49 [RFC PATCH] block: warn if blk_stack_limits() undermines atomicity Mike Snitzer
2010-02-23 17:10 ` Martin K. Petersen [this message]
2010-02-23 19:32   ` Mike Snitzer
2010-02-24  0:12     ` Martin K. Petersen

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=yq1635nop2j.fsf@sermon.lab.mkp.net \
    --to=martin.petersen@oracle.com \
    --cc=hch@infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=snitzer@redhat.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.