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authorSteven Danneman <steven.danneman@isilon.com>2009-05-04 15:02:17 -0700
committerSteven Danneman <steven.danneman@isilon.com>2009-05-04 15:02:17 -0700
commitc49730e15bd6b9b1d59e4ef271f4512d5a07c8b3 (patch)
treec2617174cbd418eb6e581c5e5f1404cbdaa337b6 /source3/libsmb
parent72bd5ff9833677c3567cd1582d5dd5fbb4001e90 (diff)
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s3:onefs.so fix issue with missing entries when enumerating directories
This bug prompted several, fairly large changes to the of OneFS's readdirplus() within Samba. One fundamental problem is that we kept our cache cursor pointed at the next entry to be returned from onefs_readdir(), while the resume cookie needed to refill the cache such that our cursor would be on this entry, was located in the previous cache entry. This meant that to correctly handle seekdir() cases which could be found within the existing cache, and cases where a cache reload was needed, required that the cache always hold at least two entries: the entry we wished to return, and the previous entry which held the resume cookie. Since the readdirplus() syscall gives us no guarantee that it will always return these two direntries, there was a fundamental problem with this design. To fix this problem, I have rearchitected the onefs_readdir() path to keep its pointer on the entry which contains the resume_cookie, not the entry which will be returned next. Essentially, I changed onefs_readdir() from a "return an entry then increment the cursor" model to "increment the cursor then return an entry". By doing this, we only require that a single entry be within the cache: the entry containing the resume cookie. Second, there have been numerous off-by-one bugs in my implementation of onefs_seekdir() which did a mapping between the 64-bit resume cookie returned by readdirplus() and its own monotonically increasing "location" offset. Furthermore, this design caused a somewhat frequent waste of cycles, as in some cases we'd need to re-enumerate the entire directory to recover the current "location" from an old resume cookie. As this code was somewhat difficult to understand, prone to bugs, and innefficient in some cases I decided it was better to wholesale replace it now, rather than later. It is possible to algorithmically map the 64-bit resume cookies from readdirplus() into 32-bit offset values which SMB requires. The onefs.so module now calls into a system library to do this conversion. This greatly simplifies both the seekdir() and telldir() paths and is more efficient.
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