Re: [PATCH] tmpfs: add padding to tmpfs_dirent structure

[Sergio Lopez]

El Wed, 19 May 2010 23:32:37 +0200
Samuel Thibault <samuel.thibault@gnu.org> escribió:

> Sergio Lopez, le Wed 19 May 2010 17:33:39 +0200, a écrit :
> > El Wed, 19 May 2010 16:05:27 +0200
> > Carl Fredrik Hammar <hammy.lite@gmail.com> escribió:
> > 
> > > On Tue, May 18, 2010 at 04:19:34PM +0200, Sergio Lopez wrote:
> > > > 
> > > > This patch adds some padding to tmpfs_dirent structure as it's
> > > > suggested in the wiki
> > > > (http://www.gnu.org/software/hurd/hurd/translator/tmpfs.html).
> > > > 
> > > 
> > > It seems Samuel beat you to it back in January: see commit 97c569.
> > > 
> > 
> > Humm... I didn't see that. Anyway, I think that change should be
> > reverted and the assertion in diskfs_get_directs removed.
> 
> Err, why removing it?  Isn't there a need for the whole struct dirent
> structure to be allocated or something like that?  (Which probably was
> the reason for the assertion).
> 

diskfs_get_directs needs to allocate a buffer and fill it with dirent
entries to describe the contents from the requested directory. The size
of this buffer is dn_stat.st_size plus two dirent structures (to hold
"." and "..").

The code seems to assume that dn_stat.st_size represents the size of a
collection of tmpfs_dirent entries, so it needs to check that this
structure is the same size or bigger than dirent, to ensure the buffer
is big enough.

But, in diskfs_direnter_hard, dn_stat.st_size is actually increased
with the value of dirent (and not tmpfs_dirent), so there's no need to
worry about the sizes of those structures.