On 2012-07-24 21:48 Christoph Hellwig <hch@xxxxxxxxxxxxx> Wrote:
>On Tue, Jul 24, 2012 at 08:44:27PM +0800, majianpeng wrote:
>> On 2012-05-29 16:56 majianpeng <majianpeng@xxxxxxxxx> Wrote:
>> >The size of block-device is larger than 16TB, and the os is 32bit.
>> >If the offset of read/write is larger then 16TB. The index of address_space will
>> >overflow and supply data from low offset instead.
>
>We can't support > 16TB block device on 32-bit systems with 4k page
>size, just like we can't support files that large.
>
>For filesystems the s_maxbytes limit of MAX_LFS_FILESIZE takes care of
>that, but it seems like we miss that check for block devices.
>
>The proper fix is to add that check (either via s_maxbytes or by
>checking MAX_LFS_FILESIZE) to generic_write_checks and
>generic_file_aio_read (or a block device specific wrapper)
>
/* Page cache limit. The filesystems should put that into their s_maxbytes
limits, otherwise bad things can happen in VM. */
#if BITS_PER_LONG==32
#define MAX_LFS_FILESIZE (((u64)PAGE_CACHE_SIZE << (BITS_PER_LONG-1))-1)
#elif BITS_PER_LONG==64
#define MAX_LFS_FILESIZE 0x7fffffffffffffffUL
#endif
If we used MAX_LFS_FILESIZE to limit the block-device, so in 32bit-os, the size of block is
only 8T -1.
But in function do_generic_file_read():
>>index = *ppos >> PAGE_CACHE_SHIFT;
index is unsigned long type. So the ppos can 16T -1.
But the comment said:
>>/* Page cache limit. The filesystems should put that into their s_maxbytes
>> limits, otherwise bad things can happen in VM. */
Why ?
Thanks !
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