linux-kernel - Re: [PATCH 1/2] zpool: define and use max type length

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Date:	Tue, 18 Aug 2015 22:20:03 -0400
From:	Dan Streetman <ddstreet@...e.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Seth Jennings <sjennings@...iantweb.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	kbuild test robot <fengguang.wu@...el.com>
Subject: Re: [PATCH 1/2] zpool: define and use max type length

On Tue, Aug 18, 2015 at 6:38 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Tue, 18 Aug 2015 16:06:00 -0400 Dan Streetman <ddstreet@...e.org> wrote:
>
>> Add ZPOOL_MAX_TYPE_NAME define, and change zpool_driver *type field to
>> type[ZPOOL_MAX_TYPE_NAME].  Remove redundant type field from struct zpool
>> and use zpool->driver->type instead.
>>
>> The define will be used by zswap for its zpool param type name length.
>>
>
> Patchset is fugly.  All this putzing around with fixed-length strings,
> worrying about overflow and is-it-null-terminated-or-isnt-it.  Shudder.
>
> It's much better to use variable-length strings everywhere.  We're not
> operating in contexts which can't use kmalloc, we're not
> performance-intensive and these strings aren't being written to
> fixed-size fields on disk or anything.  Why do we need any fixed-length
> strings?
>
> IOW, why not just replace that alloca with a kstrdup()?

for the zpool drivers (zbud and zsmalloc), the type is actually just
statically assigned, e.g. .type = "zbud", so you're right the *type is
better than type[].  I'll update it.

>
>> --- a/include/linux/zpool.h
>> +++ b/include/linux/zpool.h
>>
>> ...
>>
>> @@ -79,7 +77,7 @@ static struct zpool_driver *zpool_get_driver(char *type)
>>
>>       spin_lock(&drivers_lock);
>>       list_for_each_entry(driver, &drivers_head, list) {
>> -             if (!strcmp(driver->type, type)) {
>> +             if (!strncmp(driver->type, type, ZPOOL_MAX_TYPE_NAME)) {
>
> Why strncmp?  Please tell me these strings are always null-terminated.

Yep, you're right.  The driver->type always is, and the type param is
passed in from sysfs, which we can rely on to be null-terminated.

>
>
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