Re: [PATCH 18/29] sysctl: Normalize the root_table data structure.

[Eric W. Biederman]

Lucian thanks for the review.

Lucian Adrian Grijincu <lucian.grijincu@xxxxxxxxx> writes:

> On Fri, Jan 27, 2012 at 6:51 AM, Eric W. Biederman
> <ebiederm@xxxxxxxxxxxx> wrote:
>> Every other directory has a .child member and we look at the .child
>> for our entries. ÂDo the same for the root_table.
>>
>> Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
>> ---
>> Âfs/proc/proc_sysctl.c | Â 15 +++++++++++----
>> Â1 files changed, 11 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
>> index 7e96a26..88d1b06 100644
>> --- a/fs/proc/proc_sysctl.c
>> +++ b/fs/proc/proc_sysctl.c
>> @@ -25,7 +25,14 @@ void proc_sys_poll_notify(struct ctl_table_poll *poll)
>> Â Â Â Âwake_up_interruptible(&poll->wait);
>> Â}
>>
>> -static struct ctl_table root_table[1];
>> +static struct ctl_table root_table[] = {
>> + Â Â Â {
>> + Â Â Â Â Â Â Â .procname = "",
>> + Â Â Â Â Â Â Â .mode = S_IRUGO|S_IXUGO,
>
> Why not: .mode = S_IFDIR|S_IRUGO|S_IXUGO ?
>
> You change it later and add IFDIR in patch 22/29 because of this
> change (from 22/29):
> -	if (!table->child) {
> +	if (!S_ISDIR(table->mode)) {
>
> but if might as well be done here.

Actually doing not adding S_IFDIR here is important for keeping the
notion of changing one logical thing at a time.

I see normalizing this table early as deliberately emphasizing that we
started using S_IFDIR later.

>> + Â Â Â Â Â Â Â .child = &root_table[1],
>> + Â Â Â },
>> + Â Â Â { }
>> +};
>> Âstatic struct ctl_table_root sysctl_table_root;
>> Âstatic struct ctl_table_header root_table_header = {
>> Â Â Â Â{{.count = 1,
>> @@ -319,7 +326,7 @@ static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
>> Â Â Â Â Â Â Â Âgoto out;
>> Â Â Â Â}
>
> Somewhere above we have
>   struct ctl_table *table = PROC_I(inode)->sysctl_entry;
> and sysctl_entry can take two values:
>    - NULL: fs/proc/inode.c:proc_alloc_inode()
>    - a non-NULL table in: proc_sys_make_inode()
>
> The only inode that can be passed to proc_sys_lookup that can have
> table=NULL is the root inode.
> In that case head will be &root_table_header.
>
>
> So head->ctl_table[1] == root_table_header.ctl_table[1] == root_table[1].

Yes.

>> - Â Â Â table = table ? table->child : head->ctl_table;
>> + Â Â Â table = table ? table->child : &head->ctl_table[1];
>
> I think this could be improved to something like this:
> /* table == NULL only for the procfs root directory */
> table = table ? table->child : &root_table[1];
>
>
> It's not that important, as this code will go away in a few patches.

Good catch.  I had to ask myself after I read this why the code wasn't
pointing at root_table already.  The answer as it turns out was because
it was static in kernel/sysctl.c until my earlier patches and I simply
missed the opportunity.

>> Â Â Â Âp = find_in_table(table, name);
>> Â Â Â Âif (!p) {
>> @@ -510,7 +517,7 @@ static int proc_sys_readdir(struct file *filp, void *dirent, filldir_t filldir)
>> Â Â Â Â Â Â Â Âgoto out;
>> Â Â Â Â}
>>
>> - Â Â Â table = table ? table->child : head->ctl_table;
>> + Â Â Â table = table ? table->child : &head->ctl_table[1];
>
> Similar.

Agreed.  At this point in the game since this code does go away I don't
think it is worth making the change now. But I will keep it in mind
and I you have definitely spotted an opportunity missed in this
patchset.

Eric
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