On 4/25/15 5:52 AM, Jilles Tjoelker wrote:
On Fri, Apr 24, 2015 at 04:28:12PM -0400, John Baldwin wrote:
Yes, this isn't at all safe.  There's no guarantee whatsoever that
the offset on the directory fd that isn't something returned by
getdirentries has any meaning.  In particular, the size of the
directory entry in a random filesystem might be a different size
than the structure returned by getdirentries (since it converts
things into a FS-independent format).
This might work for UFS by accident, but this is probably why ZFS
doesn't work.
However, this might be properly fixed by the thing that ino64 is
doing where each directory entry returned by getdirentries gives
you a seek offset that you _can_ directly seek to (as opposed to
seeking to the start of the block and then walking forward N
entries until you get an inter-block entry that is the same).
The ino64 branch only reserves space for d_off and does not use it in
any way. This is appropriate since actually using d_off is a major
feature addition.

A proper d_off would still be useful even if UFS's readdir keeps masking
off the offset so a directory read always starts at the beginning of a
512-byte directory block, since this allows more distinct offset values
than safely using getdirentries()'s *basep. With d_off, one outer loop
must read at least one directory block to avoid spinning indefinitely,
while using getdirentries()'s *basep requires reading the whole
getdirentries() buffer.

Some Linux filesystems go further and provide a unique d_off for each

Another idea would be to store the last d_ino instead of dd_loc into the
struct ddloc. On seekdir(), this would seek to loc_seek as before and
skip entries until that d_ino is found, or to the start of the buffer if
not found (and possibly return some entries again that should not be
returned, but Samba copes with that).

yes.. though maybe a hash of hte inode number and the name may be a better thing to search on..

I need to check on your statement about samba to see if its true for 3.6..

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