Le Fri, 29 Aug 2008 10:51:10 +0200,
Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxxxxxxxxx> a écrit :
> So, who is doing the bounce buffering of the bio page when it's stored
> in ZONE_HIGHMEM ? Is it safe for a block driver to blindly use
> rq->buffer without knowing if the bio's page is in HIGHMEM or not ?
After some RTFM, from Documentation/block/biodoc.txt:
==
The buffer field is just a virtual address mapping of the current
segment of the i/o buffer in cases where the buffer resides in
low-memory. For high memory i/o, this field is not valid and must not
be used by drivers.
==
So, why is sbull using this ? There also some in-tree drivers using
rq->buffer:
drivers/block/z2ram.c
drivers/block/swim3.c
drivers/block/xd.c
...
Am I missing something ?
BTW, about the "buffer" field, Documentation/block/request.txt says:
char *buffer D Map of first segment, also see
section on bouncing SECTION
But I don't see where is located this « section on bouncing SECTION ».
Thanks,
Thomas
--
Thomas Petazzoni, Free Electrons
Kernel, drivers and embedded Linux development,
consulting, training and support.
http://free-electrons.com
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