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LWN.net Weekly Edition for May 16, 2013
A look at the PyPy 2.0 release
PostgreSQL 9.3 beta: Federated databases and more
LWN.net Weekly Edition for May 9, 2013
(Nearly) full tickless operation in 3.10
> If a file is removed from or added to the directory after the most recent call to opendir() or rewinddir(), whether a subsequent call to readdir_r() returns an entry for that file is unspecified.
Which presumably implies that if a file is not added or removed after opendir, then readdir will return it precisely once. That is certainly how I understand it.
Throwing one away
Posted Sep 21, 2012 23:06 UTC (Fri) by nix (subscriber, #2304)
(e.g. in the scheme I sketched above, if a readdir requester's random-cookie/filename->DIR* entry was expired by the server and the name the readdir requester passed was missing from the directory, readdir would simply start passing back filenames from the start of the directory over again. This does mean that under extreme load, so the cookies kept expiring, and seriously extreme modification rates of a sufficiently huge directory, so that at least one name was deleted while being readdir()ed and while its cookie expired on every pass through the directory, readdir() might never come to an end -- but that's possible under extreme modification rates anyway, even on local filesystems, and this is a pathological case that's unlikely to occur in practice. To be honest, given that bugs in which filenames were persistently omitted if they were in the wrong place in the directory persisted in the BSDs for something like thirty years, it seems that programs' actual requirements of readdir() are rather less extreme than the guarantees!)
Posted Sep 27, 2012 19:09 UTC (Thu) by cras (guest, #7000)
Posted Oct 5, 2012 18:56 UTC (Fri) by foom (subscriber, #14868)
>> 3. the application could be offered an interface for atomic directory
>> reads that requires the application to provide sufficient memory in a
>> single contiguous buffer (making it thread-safe in the same go).
>Actually, you can do this today, if you use the underlying
>sys_getdents64 system call. But the application would have to
>allocate potentially a very large amount of userspace memory.
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