On Wed, Feb 11, 2009 at 12:48:16AM -0500, Andreas Dilger wrote:
>
> I'm glad that the MAX_REC_LEN value is being kept, because "0" is
> too easily hit due to disk corruption.
>
I'm not too worried about that, actually. If there is a disk
corruption, we will detect it easily enough no matter which encoding
we use. I am thinking though that neither 65535 nor 0 is the best way
of encoding 65536. In fact, I would suggest the encoding 0x01.
Specifically, I suggest:
(rec_len & 65532) | ((rec_len >> 16) & 3)
This encodes valid rec_len values in the range 0 through 2**18-4, and
allows for maximum block sizes of up to 256k. To retain backwards
compatibility, and to allow for a 256k blocksize, we can have a
special case where a rec_len of either 0 or 65535 means
EXT4_BLOCK_SIZE(s).
It's unlikely we'll see VM pages of up to 256k, but at some point we
might find that the Linux VM has been enhanced to support filesystem
block sizes > than the VM page size, at which point it might be useful
for some applications to allow very large filesystem block sizes.
- Ted
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