On 01.07.2014 15:00, Ben Hoyt wrote:
> I'm leaning towards preferring #2 (Nick's proposal) because it solves
> or gets around the caching issue. My one concern is error handling. Is
> it an issue if scandir's __next__ can raise an OSError either from the
> readdir() call or the call to stat()? My thinking is probably not. In
> practice, would it ever really happen that readdir() would succeed but
> an os.stat() immediately after would fail? I guess it could if the
> file is deleted, but then if it were deleted a microsecond earlier the
> readdir() would fail anyway, or not? Or does readdir give you a
> consistent, "snap-shotted" view on things?
No need for a microsecond-timed deletion -- a directory with +r but
without +x will allow you to list the entries, but stat calls on the
files will fail with EPERM:
$ ls -l
drwxr--r--. 2 root root 60 1. Jul 16:52 test
$ sudo ls -l test
total 0
-rw-r--r--. 1 root root 0 1. Jul 16:52 foo
$ ls test
ls: cannot access test/foo: Permission denied
total 0
-????????? ? ? ? ? ? foo
$ stat test/foo
stat: cannot stat ‘test/foo’: Permission denied
I had the idea to treat a failing lstat() inside scandir() as if the
entry wasn’t found at all, but in this context, this seems wrong too.
regards,
jwi
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