On Dec 15, 2006  14:37 -0800, Ulrich Drepper wrote:
quoted text
> Andreas Dilger wrote:
> >IMHO, once part of the information is optional, why bother making ANY
> >of it required?  Consider "ls -s" on a distributed filesystem that has
> >UID+GID mapping.  It doesn't actually NEED to return the UID+GID to ls
> >for each file, since it won't be shown, but if that is part of the 
> >"required" fields then the filesystem would have to remap each UID+GID
> >on each file in the directory.  Similar arguments can be made for "find"
> >with various options (-atime, -mtime, etc) where any one of the "required"
> >parameters isn't needed.
> 
> The kernel at least has to clear the fields in the stat structure in any 
> case.  So, if information is easily available, why add another 'if' in 
> the case if the real information can be filled in just as easily?


The kernel doesn't necessarily have to clear the fields.  The per-field
valid flag would determine is that field had valid data or garbage.

That said, there is no harm in the kernel/fs filling in additional fields
is they are readily available.  It would be up to the caller to NOT ask
for fields that it doesn't need, as that _might_ cause additional work
on the part of the filesystem.  If the kernel returns extra valid fields
(because they are "free") that the application doesn't use, no harm done.

quoted text
> >I used to think this also, but even though Lustre supplies d_type info
> >GNU ls will still do stat operations because "ls --color" depends on
> >st_mode in order to color executable files differently.
> 
> Right, and only executables.
> 
> You can easily leave out the :ex=*** part of LS_COLORS.

Tell that to every distro maintainer, and/or try to convince the upstream
"ls" maintainers to change this. :-)

quoted text
> I don't think it's useful to introduce a new system call just to have 
> this support.

It isn't just to fix the ls --color problem.  There are lots of other
apps that need some stat fields and not others.  Also, implementing
the compatibility support for this (statlite->stat(), flags=$all_valid)
is trivial, if potentially less performant (though no worse than today).

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.

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