linux-ext4 - Re: [PATCH RFC] block: use discard if possible in blkdev_issue

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 17 Feb 2014 22:44:47 -0500
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	"Martin K. Petersen" <martin.petersen@...cle.com>,
	linux-fsdevel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH RFC] block: use discard if possible in blkdev_issue_discard()

>>>>> "Ted" == Theodore Ts'o <tytso@....edu> writes:

Ted> Ultimately the storage device (or host OS) can always decide to
Ted> deprovision the space if it is given a write of all zeroes; there's
Ted> nothing in the specs that say anything at all about performance
Ted> considerations, or what the back-end storage decides to do in order
Ted> to handle a particular write command, so long as a subsequent read
Ted> returns the correct data.

Well, that has changed a bit with the logical block provisioning bits in
SCSI. That's why I brought up the allocation/deallocation assumptions in
the existing two blkdev_issue_foo() calls.

Ted> Does that make sense?

Yeah. So deprovision with guaranteed zero on read is what you're
after. I'll chew on that a bit tomorrow.

Ted> What does "anchored" mean?  Does is it the equivalent of using
Ted> fallocate() to allocate the block, but it's marked uninitialized so
Ted> any attempt to read it returns zeroes?

It means that any allocations internal to the storage device which are
required to subsequently perform a write to that block have been
made. So it's a way to reserve space without actually writing the
blocks. Whether reading an anchored block returns zeroes or something
else depends on the usual twisted maze of conflicting and confusing
flags.

-- 
Martin K. Petersen	Oracle Linux Engineering
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html