Re: [PATCH 1/2] disk: Add support for device-specific malloc function

[Andrei Borzenkov]

22.02.2016 17:02, Leif Lindholm пишет:
> On Mon, Feb 22, 2016 at 10:57:24AM +0300, Andrei Borzenkov wrote:
>> 19.02.2016 19:18, Leif Lindholm пишет:
>>> Some disk types have allocation requirements beyond normal grub_malloc.
>>> Add a function pointer to grub_disk_t and a wrapper function in
>>> kern/disk.c making use of that function if available, to enable these
>>> disk drivers to implement their own malloc.
>>
>> The problem is not (only) grub_disk_read_small(), but this part in
>> grub_disk_read:
>>
>>       if (agglomerate)
>>         {
>>           grub_disk_addr_t i;
>>
>>           err = (disk->dev->read) (disk, transform_sector (disk, sector),
>>                                    agglomerate << (GRUB_DISK_CACHE_BITS
>>                                                    + GRUB_DISK_SECTOR_BITS
>>                                                    - disk->log_sector_size),
>>                                    buf);
>>
>> which reads directly into user supplied buffer. May be we can allocate
>> contiguous cache block here but put pointers to multiple chunks inside
>> it. Possible implementation is to have second layer of reference counted
>> memory blocks with cache entries containing pointer + offset into them.
> 
> Whoops!
> 
> Understood.
> 
> So how about merging the two concepts?
> Including a patch to go with (after) the previous two to catch any
> remaining unaligned accesses in grub_efidisk_readwrite().
> With this applied, I get no fixups from a normal Linux boot (linux +
> initrd), but see them when exploring filesystems from the command
> line.
> 
> Whilst a bit clunky, this seems much short-term preferable to going
> back and redesigning the disk subsystem to understand that alignment
> matters. Although given the number of exceptions we seem to be
> amassing, that does not sound like a bad idea for future.
> 

Could you test attached patch with your alignment fixes on top. This
implements my idea of using shared buffers. Seems to work in naive testing.

disk-direct-cache-read.patch
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