On 6/28/22 16:09, Michael Schmitz wrote:
On 29/06/22 09:50, Arnd Bergmann wrote:
On Tue, Jun 28, 2022 at 11:03 PM Michael Schmitz
<schmitzmic@xxxxxxxxx> wrote:
On 28/06/22 19:03, Geert Uytterhoeven wrote:
The driver allocates bounce buffers using kmalloc if it hits an
unaligned data buffer - can such buffers still even happen these days?
No idea.
Hmmm - I think I'll stick a WARN_ONCE() in there so we know whether this
code path is still being used.
kmalloc() guarantees alignment to the next power-of-two size or
KMALLOC_MIN_ALIGN, whichever is bigger. On m68k this means it
is cacheline aligned.
And all SCSI buffers are allocated using kmalloc? No way at all for user
space to pass unaligned data?
(SCSI is a weird beast - I have used a SCSI DAT tape driver many many
years ago, which broke all sorts of assumptions about transfer block
sizes ... but that might actually have been in the v0.99 days, many
rewrites of SCSI midlevel ago).
Just being cautious, as getting any of this tested will be a stretch.
An example of a user space application that passes an SG I/O data buffer
to the kernel that is aligned to a four byte boundary but not to an
eight byte boundary if the -s (scattered) command line option is used:
https://github.com/osandov/blktests/blob/master/src/discontiguous-io.cpp
Bart.
