linux-ext4 - Re: [PATCH] ext4: don't work without procfs

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Date:	Tue, 4 Oct 2011 13:33:53 +0200 (CEST)
From:	Lukas Czerner <lczerner@...hat.com>
To:	yargil@...e.fr
cc:	Lukas Czerner <lczerner@...hat.com>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: don't work without procfs

On Tue, 4 Oct 2011, yargil@...e.fr wrote:

> Selon Lukas Czerner <lczerner@...hat.com>:
> 
> > On Mon, 3 Oct 2011, Yargil wrote:
> >
> > > Regression from commit dd68314ccf3fb918c1fb6471817edbc60ece4b52
> >
> > Hi,
> >
> > the commit you've mentioned does not have anything to do with procfs.
> > Maybe you meant commit
> >
> > c9de560ded61faa5b754137b7753da252391c55a
> > 	ext4: Add multi block allocator for ext4
> >
> > which adds multi block allocator for ext4 (mballoc.c) and has been added
> > in Jan 29 2008.
> >
> > > ---
> > >  fs/ext4/super.c |    8 ++++++++
> > >  1 files changed, 8 insertions(+), 0 deletions(-)
> > >
> > > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > > index 44d0c8d..8e7298d 100644
> > > --- a/fs/ext4/super.c
> > > +++ b/fs/ext4/super.c
> > > @@ -53,7 +53,9 @@
> > >  #define CREATE_TRACE_POINTS
> > >  #include <trace/events/ext4.h>
> > >
> > > +#ifdef CONFIG_PROC_FS
> > >  static struct proc_dir_entry *ext4_proc_root;
> > > +#endif
> >
> > This is not needed I think, since proc_dir_entry is defined in
> > linux/proc_fs.h even if CONFIG_PROC_FS is not defined.
> >
> > >  static struct kset *ext4_kset;
> > >  static struct ext4_lazy_init *ext4_li_info;
> > >  static struct mutex ext4_li_mtx;
> > > @@ -812,9 +814,11 @@ static void ext4_put_super(struct super_block *sb)
> > >  		es->s_state = cpu_to_le16(sbi->s_mount_state);
> > >  		ext4_commit_super(sb, 1);
> > >  	}
> > > +#ifdef CONFIG_PROC_FS
> > >  	if (sbi->s_proc) {
> > >  		remove_proc_entry(sb->s_id, ext4_proc_root);
> >
> > This function exists even if CONFIG_PROC_FS is not defined.
> >
> > #define remove_proc_entry(name, parent) do {} while (0)
> >
> >
> > >  	}
> > > +#endif
> > >  	kobject_del(&sbi->s_kobj);
> > >
> > >  	for (i = 0; i < sbi->s_gdb_count; i++)
> > > @@ -4984,9 +4988,11 @@ static int __init ext4_init_fs(void)
> > >  	ext4_kset = kset_create_and_add("ext4", NULL, fs_kobj);
> > >  	if (!ext4_kset)
> > >  		goto out6;
> > > +#ifdef CONFIG_PROC_FS
> > >  	ext4_proc_root = proc_mkdir("fs/ext4", NULL);
> >
> > The same here
> >
> > static inline struct proc_dir_entry *proc_mkdir(const char *name,
> > 	struct proc_dir_entry *parent) {return NULL;}
> >
> >
> > >  	if (!ext4_proc_root)
> > >  		goto out5;
> > However this is wrong, because in case that procfs is not compiled in
> > ext4_proc_root will be NULL, but there is no reason to error out in this
> > case.
> >
> > The question is whether we should error out in case that it fails even
> > if we have procfs compiled in. I am slightly in favour of just printing
> > a warning in !CONFIG_PROC_FS case.
> >
> > Also this is probably why you blame commit
> > dd68314ccf3fb918c1fb6471817edbc60ece4b52 for the regression, since this
> > check was added with this commit. But I think that there is no reasong
> > to #ifdef everything procfs related.
> 
> I did that to avoid warning. But if printing warning is not a problem then the
> only part of code to be #ifdef is the test of the return value of proc_mkdir in
> the ext4_init_fs function.

Exactly, it has the advantage of not spawning #ifdefs in super.c and the
advantage of not preventing the mount in case that the proc_mkdir() fails
for some reason, because we actually do not need that for file system to
work properly.

Thanks!
-Lukas

> 
> >
> >
> > > +#endif
> > >
> > >  	err = ext4_init_feat_adverts();
> > >  	if (err)
> > > @@ -5022,8 +5028,10 @@ out2:
> > >  out3:
> > >  	ext4_exit_feat_adverts();
> > >  out4:
> > > +#ifdef CONFIG_PROC_FS
> > >  	remove_proc_entry("fs/ext4", NULL);
> >
> > same here.
> >
> > >  out5:
> > > +#endif
> > >  	kset_unregister(ext4_kset);
> > >  out6:
> > >  	ext4_exit_system_zone();
> > >
> >
> > -Lukas
> >
> 
> 
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