Messages in this thread | | | From | Goswin von Brederlow <> | Subject | Re: [fuse-devel] FS block count, size and seek offset? | Date | Mon, 18 Jun 2007 10:55:39 +0200 |
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"David Brown" <dmlb2000@gmail.com> writes:
> I was looking at various file systems and how they return > stat.st_blocks and stat.st_size for directories and had some questions > on how a fuse filesystem is supposed to implement readdir with the > seek offset when trying to union two directories together. > > Is the offset a byte offset into the DIR *dp? or is it the struct > dirent size (which is relative based on the name of the file) into the > dir pointer?
I think it is totaly your call what you store in it. Only requirement is that you never pass 0 to the filler function.
off_t is 64bit so storing DIR* in it should be no problem. Or a pointer to
struct UnionDIR { DIR *dp; struct UnionDIR *next; }
> Also, if you want to be accurate when you stat a directory that's > unioned in the fuse file system how many blocks should one return? > Since each filesystem seems to return different values for size and > number of blocks for directories. I know I could just say that its not > supported with my filesystem built using fuse... but I'd like to at > least try to be accurate.
You could add them up and round it to some common block size (if they differ). But I don't think it maters and nothing uses that info.
What is more important is the link count. For example find uses the link count to know how many subdirs a directory has. Once it found that many it assumes there are no more dirs and saves on stat() calls.
> Is it accurate to assume that the size or number of blocks returned > from a stat will be used to pass a seek offset? > > When does fuse use the seek offset?
Afaik never. The offset is only stored for the next readdir call but never used inside fuse.
> These are the number of blocks and size on an empty dir. > ext3 > size 4096 nblocks 8 > reiserfs > size 48 nblocks 0 > jfs > size 1 nblocks 0 > xfs > size 6 nblocks 0 > > Any help to figure out how to union two directories and return correct > values would be helpful.
Why don't you use the existing fuse-unionfs?
> Thanks, > - David Brown > > P.S. maybe a posix filesystem interface manual would be good?
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