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Re: genfs_gop_write_rwmap


On Tue, Feb 10, 2009 at 05:23:53PM +0900, YAMAMOTO Takashi wrote:
> can you explain why genfs_gop_write_rwmap is necessary?
> thanks.

I think i've explained it earlier on the list but its to accomodate updating
the buffers i get passed by genfs in UDF. This may sound silly, but the UDF
file system needs its descriptors (like inode structures and dirents) to be
tailored explicitly to the sector written.

What happends is that when it modifies a directory entry it needs to be
written back to disc but that block will be written at a different location.
Even every UDF `dirent' has its logical block number written in it together
with a crc. So if blocks are moved around, their lba change and i need to
update it in the structure and recalculate the crc.  In theory i could copy
all the blocks but that would double the amount of dirty directory data and i
dont think thats a good idea either.

I could try to work around it another way, but i dont think it'll be prettier.

With regards,

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