Re: [PATCH] barrier patch set

[Jens Axboe]

On Fri, Mar 19 2004, Jeff Garzik wrote:
> Jens Axboe wrote:
> >Cosmetic stuff that will get ironed out. You can find the patches here:
> >
> >ftp://ftp.kernel.org/pub/linux/kernel/people/axboe/patches/v2.6/2.6.5-rc1-mm2/
> >
> >ide-barrier-2.6.5-rc1-mm2-1
> >	ide/core part
> 
> 
> WRT ATA and flush-cache...  before the IDE pieces of this patch are 
> merged, IMO it is a requirement that the entire flush-cache stuff gets a 
> review.  ide_get_error_location() is one of the important pieces 

Well what are you waiting for :-). Honestly, the bits have been "out
there" for 2 years or so, so it's not like it's anything brand new.

ide_get_error_location() is new for 2.6, I consider the 2.6 code to have
basically 100% coverage where the 2.4 one never really did...

> (great!).  Another important piece is to make sure that a drive's 
> flush-cache capability is correctly deduced and set up from the 
> identify-device.  The steps look like
> 
> - check identify-device word 83, bits 12 (flush cache) and 13 (flush 
> cache ext)
> - issue set-features command to get flush-cache into proper state 
> (enabled or disabled, as the user desires), if identify-device word 86 
> indicates it is not already in the state you seek.
> - re-read identify [packet] device page from device, make sure 
> flush-cache[-ext] is enabled.  A slacker could just make sure the 
> set-features command completed successfully, but to be 100% correct you 
> need to re-read the identify-device page.  :/
> 
> NOTE 1: these steps are specific to the flush-cache command, and are 
> only vaguely related to write caching (which must be tested-for and 
> enabled separately).  It is important to go through these steps 
> separately for write-caching and flush-cache[-ext].
> 
> Write-caching and flush-cache-command state should always be considered 
> separately, even though the two are often used together.  I want to 
> avoid the LG cdrom debacle, where not properly checking for, and setting 
> up, flush-cache resulted in turning cdroms into bricks.
> 
> NOTE 2: Don't forget to check for 0x0000 or 0xffff in word 86, of 
> __only__ identify-packet-device.  These special case meanings do not 
> appear for ATA devices, only ATAPI devices.
> 
> NOTE 3: flush-cache-ext should always be used on lba48 devices, even if 
> the request was inside the lba28 limit.
> 
> NOTE 4: flush-cache-ext does not exist on ATAPI devices.

Only ide-disk is supported. But that's some great info, I'll go over the
code this weekend and make sure we're doing ok and correct any
deviations.

-- 
Jens Axboe

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