[stgt] [PATCH] COMPARE_AND_WRITE: Fix this opcode so it works according to SBC

[Arne Redlich]

[Sending once more as vger bounced the previous mail - sorry for the duplicates]

2012/11/17 Ronnie Sahlberg <ronniesahlberg at gmail.com>
>
> After reading SBC again it becomes a lot more clear how this
> opcode works.
> Reactivate the opcode and implement it properly.
> Compare the first "number of blocks" from DATA-OUT with the existing
> content of these blocks on the LUN.
> If it compare ok, then overwrite these block on the lun with the
> next "number of blocks" from the DATA-OUT buffer.

How is atomicity guaranteed? CMIIW (it's been a while that I looked
into TGT code), but I think another backing store thread could modify
the data concurrently.

Thanks,
Arne
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