Re: [PATCH] libata: add support for READ/WRITE LONG

[Sergei Shtylyov <sshtylyov@ru.mvista.com>]

Hello.

Mark Lord wrote:

>>> The fussy bit is that these commands require a non-standard
>>> sector size, usually 520 bytes instead of 512.

>>    Which requires from the drivers to be able to turn off IDE prefetch 
>> (and maybe posting too).  I don't see that in this patch (or are you 
>> expecting them to just "snoop' the commands and do it automagically?).

> Most controllers seem to be behave well enough
> and just not muck up.  And if it fails on any "too clever" controllers,
> then no big deal -- we just switch to a controller that works instead.

   IDE controllers are generally not known as "clever" -- and that's what's 
frightening me... :-)

> This is not an essential command for normal operation.
> What it is for, is injecting errors so that we can experience
> firsthand the (excellent or crappy) error handling in the kernel
> and in applications.  And then work out and test better strategies.

> So 100% working everywhere, for an obsolete opcode, isn't really
> essential to me.  But it should work most places, and it does.

    I don't think it should *correctly* work anywhere w/prefetch on, IDE bus 
wise.  Maybe that just doesn't show up on host side (but well might have been).

>>    Again, ata_data_xfer() doesn't seem capable of performing ECC 
>> read/writes
>> -- the ECC bytes must be transferred in 8-bit mode, AFAIR. 
>> ata_data_xfer()
>> can oinly do that for optionally trailing odd byte.

> I have no idea what that was all about.  Care to explain again?

    Care to read the standards? :-/

> RWLONG transfer the ECC info 8-bits at a time, using 16-bit words
> to do so, no different from normal.  ???

    From ATA-1:

    "The transfer of the vendor specific bytes shall be one byte at a time 
over bits DD0-7 only (8-bits wide)."

> Here it is again with the whitespace not so messed up.

   I'm sorry, it seems only being messed on my side, due to format=flowed. :-/

> The READ/WRITE LONG commands are theoretically obsolete,
> but the majority of drives in existance still implement them.

> The WRITE_LONG and WRITE_LONG_ONCE commands are of particular
> interest for fault injection testing -- eg. creating "media errors"
> at specific locations on a disk.

> The fussy bit is that these commands require a non-standard
> sector size, usually 520 bytes instead of 512.

    It's 516 bytes, not 512 as you claim. Well, maybe the extra odd bytes 
don't matter anyway in this GIGO case... :-)

> This patch adds support to libata for READ/WRITE LONG commands
> issued via SG_IO/ATA_16.

> This patch was generated against a 2.6.21-rc3-git7 base:

MBR, Sergei