Re: Bug in scandir d_type

[Jeff Mahoney <jeffm@suse.com>]

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Andreas Dilger wrote:
| On Dec 07, 2004  12:54 -0500, Jeff Mahoney wrote:
|
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|>egilam@student.matnat.uio.no wrote:
|>| Hello.
|>|
|>| I am working with a program that uses scandir, using d_type to check
if a
|>| file has certain properties. It seems like that when used on
reiserfs 3.6
|>| (I haven't tried any other version), the d_type field is always 0
(zero).
|>| When the program is moved onto an ext2 partition, it works. The example
|>| program in "man scandir" works also the same way (just replace
d_name with
|>| d_type when printing out).
|>|
|>| Kernel:  2.6.8.1 with reiserfs compiled in.
|>
|>The d_type feature appears to be optional. ext[23] only supports it
|>because the feature was tacked on later, it's protected by an
|>incompatible feature bit. Most other Linux filesystems only bother
|>returning something other than DT_UNKNOWN for . and .., which is kind of
|>silly.
|>
|>In order to get the type information from the file/directory, it either
|>needs to be stored with the directory entry (disk format change
|>required), or readdir needs to load _every_ inode referenced by the
|>directory which would be an immense performance hit for such a small
|>corner case. ReiserFS has been in the mainline kernel for years now, and
|>your message is the first complaint I've seen about this feature missing.
|
|
| Doesn't reiserfs store the mode in the directory entry anyways, or is that
| only reiser4?  So the overhead of returning the filetype is virtually nil.

Reiser3 only stores the key and the name in a directory entry. I don't
know about reiser4. If that is the case, absolutely, return the type.
However, this bug report was for reiser3.

|>If you truly need the type information, a more portable solution would
|>be to stat() each filename returned. You can generate the d_type value
|>as follows:
|
|
| Which obviates the whole point of d_type, which is to get the filetype
| efficiently without hundreds of extra syscalls (which is at least part
| of what Hans wants with sys_reiser4()).

True enough, but as I said, in addition to reiser3, almost every other
filesystem returns garbage for d_type. If we don't have the information
to offer without performing what is essentially the backend of sys_stat,
I'd rather the user explicitly request it.

- -Jeff

- --
Jeff Mahoney
SuSE Labs
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