Re: ntfs: remove redundant assignments
From: Pekka J Enberg (penberg_at_cs.helsinki.fi)
Date: 05/26/05
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To: Anton Altaparmakov <aia21@cam.ac.uk> Date: Thu, 26 May 2005 09:21:46 +0300
Hi Anton,
At some point in time, I wrote:
> Index: 2.6-mm/fs/ntfs/super.c
> > ===================================================================
> > --- 2.6-mm.orig/fs/ntfs/super.c 2005-05-25 20:51:57.000000000 +0300
> > +++ 2.6-mm/fs/ntfs/super.c 2005-05-25 20:54:02.000000000 +0300
> > @@ -2283,7 +2283,7 @@
> > sb->s_flags |= MS_RDONLY | MS_NOATIME | MS_NODIRATIME;
> > #endif /* ! NTFS_RW */
> > /* Allocate a new ntfs_volume and place it in sb->s_fs_info. */
> > - sb->s_fs_info = kmalloc(sizeof(ntfs_volume), GFP_NOFS);
> > + sb->s_fs_info = kcalloc(1, sizeof(ntfs_volume), GFP_NOFS);
> > vol = NTFS_SB(sb);
> > if (!vol) {
> > if (!silent)
> > @@ -2292,28 +2292,9 @@
> > return -ENOMEM;
> > }
> > /* Initialize ntfs_volume structure. */
> > - memset(vol, 0, sizeof(ntfs_volume));
> > vol->sb = sb;
>
> The above is fine, thanks.
>
> > - vol->upcase = NULL;
> > - vol->attrdef = NULL;
> > - vol->mft_ino = NULL;
> > - vol->mftbmp_ino = NULL;
> > init_rwsem(&vol->mftbmp_lock);
> > -#ifdef NTFS_RW
> > - vol->mftmirr_ino = NULL;
> > - vol->logfile_ino = NULL;
> > -#endif /* NTFS_RW */
> > - vol->lcnbmp_ino = NULL;
> > init_rwsem(&vol->lcnbmp_lock);
> > - vol->vol_ino = NULL;
> > - vol->root_ino = NULL;
> > - vol->secure_ino = NULL;
> > - vol->extend_ino = NULL;
> > -#ifdef NTFS_RW
> > - vol->quota_ino = NULL;
> > - vol->quota_q_ino = NULL;
> > -#endif /* NTFS_RW */
> > - vol->nls_map = NULL;
On Wed, 2005-05-25 at 22:10 +0100, Anton Altaparmakov wrote:
> This is not. memset(0) is not the same as = NULL IMO. I don't care if
> the compiler thinks it is the same. NULL does not have to be 0 so I
> prefer to initialize pointers explicitly to NULL. Even more so since this
> code is not performance critical at all so I prefer clarity here.
I kind of figured out you were doing it on purpose. The fact is, NULL is
zero on _all_ Linux architectures. If it weren't, we'd have a lot of broken
code. Let me play the devils advocate here: why do you memset() (now
kcalloc()) in the first place?
At some point in time, I wrote:
> > Index: 2.6-mm/fs/ntfs/index.c
> > ===================================================================
> > --- 2.6-mm.orig/fs/ntfs/index.c 2005-05-25 20:51:57.000000000 +0300
> > +++ 2.6-mm/fs/ntfs/index.c 2005-05-25 21:07:38.000000000 +0300
> > @@ -40,16 +40,8 @@
> >
> > ictx = kmem_cache_alloc(ntfs_index_ctx_cache, SLAB_NOFS);
> > if (ictx) {
> > + memset(ictx, 0, sizeof(*ictx));
> > ictx->idx_ni = idx_ni;
> > - ictx->entry = NULL;
> > - ictx->data = NULL;
> > - ictx->data_len = 0;
> > - ictx->is_in_root = 0;
> > - ictx->ir = NULL;
> > - ictx->actx = NULL;
> > - ictx->base_ni = NULL;
> > - ictx->ia = NULL;
> > - ictx->page = NULL;
On Wed, 2005-05-25 at 22:10 +0100, Anton Altaparmakov wrote:
> Again, as above, I prefer to have the explicit = NULL instead of a memset.
There's a simple reason why I don't like explicit assignments: it's way too
easy to forget to initialize something.
Pekka
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