Re: [patch] ext2_fill_super breakage

Brian Gerst
2002-03-28T18:14:26Z

Andrew Morton wrote:
>
> Brian Gerst wrote:
> >
> > Andrew Morton wrote:
> > > In 2.5.7 there is a thinko in the allocation and initialisation
> > > of the fs-private superblock for ext2. It's passing the wrong type
> > > to the sizeof operator (which of course gives the wrong size)
> > > when allocating and clearing the memory.
> > >
> > > Lesson for the day: this is one of the reasons why this idiom:
> > >
> > > some_type *p;
> > >
> > > p = malloc(sizeof(*p));
> > > ...
> > > memset(p, 0, sizeof(*p));
> > >
> > > is preferable to
> > >
> > > some_type *p;
> > >
> > > p = malloc(sizeof(some_type));
> > > ...
> > > memset(p, 0, sizeof(some_type));
> > >
> > > I checked the other filesystems. They're OK (but idiomatically
> > > impure). I've added a couple of defensive memsets where
> > > they were missing.
> >
> > I'm not sure I follow you here. Compiling this code (gcc 2.96):
> >
> > int foo1(void) { return sizeof(struct ext2_sb_info); }
> > int foo2(struct ext2_sb_info *sbi) { return sizeof(*sbi); }
>
> The current code is using sizeof(ext2_super_block) for
> something which is of type ext2_sb_info.
>
> The stylistic change tends to provide insulation from the
> above bug.

Doh. Point taken.

--

Brian Gerst