[Python-Dev] [Python-checkins] cpython: Backed out changeset 36f2e236c601: For some reason, rewinddir() doesn't work as

[Charles-François Natali]

>> Can rewinddir() end up touching the filesystem to retrieve data? I
>> noticed that your previous change (the one this checkin reverted)
>> moved it outside the GIL release macros.
>
> It just resets a position count. (in glibc).

Actually, it also calls lseek() on the directory FD:
http://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/rewinddir.c;hb=HEAD

But lseek() doesn't (normally) perform I/O, it just sets an offset in
the kernel file structure:
http://lxr.free-electrons.com/source/fs/read_write.c#L38

For example, it's not documented to return EINTR.

Now, one could imagine that the kernel could do some read-ahead or
some other magic things when passed SEEK_DATA or SEEK_HOLE, but
seeking at the beginning of a directory FD should be fast.

Anyway, I ended up reverting this change, because for some reason this
broke OpenIndiana buildbots (maybe rewinddir() is a no-op before
readdir() has been called?).

Cheers,

cf