fs/udf: vm pages "overlap" while reading large dir

Andriy Gapon avg at icyb.net.ua
Tue Feb 12 12:33:24 UTC 2008

on 12/02/2008 13:47 Poul-Henning Kamp said the following:
> In message <47B181F2.2070808 at icyb.net.ua>, Andriy Gapon writes:
>> 2.3. this code passes to bread blkno that is calculated as 4*sector,
>> where sector is a number of a physical 2048-byte sector. [**]
>> [**] - I think that this is a requirement of buffcache system, because
>> internally it performs many calculations that seem to assume that block
>> size is always 512.
> Yes, the buf-cache works in 512 bytes units throughout.
>> 3.1. for a fresh buf getlbk would assign the following:
>> bsize = bo->bo_bsize;
>> offset = blkno * bsize;
> That's clearly wrong.
> We need to assert that the blkno is aligned to the start of a sector
> and use the 512 byte units, so I guess it would be:
>     offset = dbtob(blkno);
>     KASSERT(!(offset & (bsize - 1)), ("suitable diagnostic"));

Thank you for this very insightful and neat suggestion!
I think that it must work but I will try test it tonight on whatever
media and FS-s I have available.
Thank you again!

P.S. hope to not get '"suitable diagnostic"' from something like msdosfs :-)

Andriy Gapon

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