[PATCH] block: Remove leading whitespace and trailing newline in elevator switch error message

[PATCH] block: Remove leading whitespace and trailing newline in elevator switch error message

[markus]

Trying to switch to a non-existing elevator currently results in garbled
dmesg output, e.g.:

 # echo "  foo" > /sys/block/sda/queue/scheduler 

elevator: type   foo not found
elevator: switch to   foo
 failed

(note the leading whitespace and unintended line break.)

Fix by removing the leading whitespace and stripping the trailing newline.

Signed-off-by: Markus Trippelsdorf <markus@trippelsdorf.de>

diff --git a/block/elevator.c b/block/elevator.c
index bf11e70f008b..3e1a42192519 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -1054,7 +1054,6 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
  */
 static int __elevator_change(struct request_queue *q, const char *name)
 {
-	char elevator_name[ELV_NAME_MAX];
 	struct elevator_type *e;
 
 	/*
@@ -1063,15 +1062,14 @@ static int __elevator_change(struct request_queue *q, const char *name)
 	if (q->mq_ops && !strncmp(name, "none", 4))
 		return elevator_switch(q, NULL);
 
-	strlcpy(elevator_name, name, sizeof(elevator_name));
-	e = elevator_get(strstrip(elevator_name), true);
+	e = elevator_get(name, true);
 	if (!e) {
-		printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
+		printk(KERN_ERR "elevator: type %s not found\n", name);
 		return -EINVAL;
 	}
 
 	if (q->elevator &&
-	    !strcmp(elevator_name, q->elevator->type->elevator_name)) {
+	    !strcmp(name, q->elevator->type->elevator_name)) {
 		elevator_put(e);
 		return 0;
 	}
@@ -1112,16 +1110,19 @@ static inline bool elv_support_iosched(struct request_queue *q)
 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
 			  size_t count)
 {
+	char elevator_name[ELV_NAME_MAX];
 	int ret;
 
 	if (!(q->mq_ops || q->request_fn) || !elv_support_iosched(q))
 		return count;
 
-	ret = __elevator_change(q, name);
+	strlcpy(elevator_name, skip_spaces(name), sizeof(elevator_name));
+	strstrip(elevator_name);
+	ret = __elevator_change(q, elevator_name);
 	if (!ret)
 		return count;
 
-	printk(KERN_ERR "elevator: switch to %s failed\n", name);
+	printk(KERN_ERR "elevator: switch to %s failed\n", elevator_name);
 	return ret;
 }
 

-- 
Markus

Re: [PATCH] block: Remove leading whitespace and trailing newline in elevator switch error message

[Bart Van Assche]

On Sat, 2017-05-06 at 07:22 +0200, markus@trippelsdorf.de wrote:
> -	ret =3D __elevator_change(q, name);
> +	strlcpy(elevator_name, skip_spaces(name), sizeof(elevator_name));

Hello Markus,

Please include the version number of a patch in the e-mail subject line whe=
n
posting a second or later version. Regarding the strlcpy() call, in the
FreeBSD strlcpy() man page I found the following: "If the src and dst strin=
gs
overlap, the behavior is undefined." Since the Linux kernel implementation =
of
strlcpy() uses memcpy() and since the ANSI C standard does not allow that
memcpy() input and output buffers overlap, please rework this code. See e.g=
.
http://pubs.opengroup.org/onlinepubs/9699919799/functions/memcpy.html

Thanks,

Bart.=

Re: [PATCH] block: Remove leading whitespace and trailing newline in elevator switch error message

[markus]

On 2017.05.08 at 15:47 +0000, Bart Van Assche wrote:
> On Sat, 2017-05-06 at 07:22 +0200, markus@trippelsdorf.de wrote:
> > -	ret = __elevator_change(q, name);
> > +	strlcpy(elevator_name, skip_spaces(name), sizeof(elevator_name));
> 
> Please include the version number of a patch in the e-mail subject line when
> posting a second or later version. Regarding the strlcpy() call, in the
> FreeBSD strlcpy() man page I found the following: "If the src and dst strings
> overlap, the behavior is undefined." Since the Linux kernel implementation of
> strlcpy() uses memcpy() and since the ANSI C standard does not allow that
> memcpy() input and output buffers overlap, please rework this code. See e.g.
> http://pubs.opengroup.org/onlinepubs/9699919799/functions/memcpy.html

I don't see how src and dst could possibly overlap here.

-- 
Markus

Re: [PATCH] block: Remove leading whitespace and trailing newline in elevator switch error message

[Bart Van Assche]

On Mon, 2017-05-08 at 18:48 +0200, markus@trippelsdorf.de wrote:
> On 2017.05.08 at 15:47 +0000, Bart Van Assche wrote:
> > On Sat, 2017-05-06 at 07:22 +0200, markus@trippelsdorf.de wrote:
> > > -	ret =3D __elevator_change(q, name);
> > > +	strlcpy(elevator_name, skip_spaces(name), sizeof(elevator_name));
> >=20
> > Please include the version number of a patch in the e-mail subject line=
 when
> > posting a second or later version. Regarding the strlcpy() call, in the
> > FreeBSD strlcpy() man page I found the following: "If the src and dst s=
trings
> > overlap, the behavior is undefined." Since the Linux kernel implementat=
ion of
> > strlcpy() uses memcpy() and since the ANSI C standard does not allow th=
at
> > memcpy() input and output buffers overlap, please rework this code. See=
 e.g.
> > http://pubs.opengroup.org/onlinepubs/9699919799/functions/memcpy.html
>=20
> I don't see how src and dst could possibly overlap here.

Hello Markus,

Sorry - I misread your patch. Since that was the only comment I had:

Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>=

Re: [PATCH] block: Remove leading whitespace and trailing newline in elevator switch error message

[Jens Axboe]

On 05/05/2017 11:22 PM, markus@trippelsdorf.de wrote:
> 
> Trying to switch to a non-existing elevator currently results in garbled
> dmesg output, e.g.:
> 
>  # echo "  foo" > /sys/block/sda/queue/scheduler 
> 
> elevator: type   foo not found
> elevator: switch to   foo
>  failed
> 
> (note the leading whitespace and unintended line break.)
> 
> Fix by removing the leading whitespace and stripping the trailing newline.

Added, thanks.

-- 
Jens Axboe

RE: [PATCH] block: Remove leading whitespace and trailing newline in elevator switch error message

[Elliott, Robert (Persistent Memory)]

> -----Original Message-----
> From: linux-block-owner@vger.kernel.org [mailto:linux-block-
> owner@vger.kernel.org] On Behalf Of markus@trippelsdorf.de
> Sent: Saturday, May 06, 2017 12:23 AM
> To: Bart Van Assche <Bart.VanAssche@sandisk.com>
> Cc: linux-block@vger.kernel.org; axboe@kernel.dk
> Subject: [PATCH] block: Remove leading whitespace and trailing
> newline in elevator switch error message
>=20
>=20
> Trying to switch to a non-existing elevator currently results in
> garbled
> dmesg output, e.g.:
>=20
>  # echo "  foo" > /sys/block/sda/queue/scheduler
>=20
> elevator: type   foo not found
> elevator: switch to   foo
>  failed
...
> @@ -1063,15 +1062,14 @@ static int __elevator_change(struct
> request_queue *q, const char *name)
>  	if (q->mq_ops && !strncmp(name, "none", 4))
>  		return elevator_switch(q, NULL);
>=20
> -	strlcpy(elevator_name, name, sizeof(elevator_name));
> -	e =3D elevator_get(strstrip(elevator_name), true);
> +	e =3D elevator_get(name, true);
>  	if (!e) {
> -		printk(KERN_ERR "elevator: type %s not found\n",
> elevator_name);
> +		printk(KERN_ERR "elevator: type %s not found\n", name);
>  		return -EINVAL;
>  	}
...
> @@ -1112,16 +1110,19 @@ static inline bool elv_support_iosched(struct
> request_queue *q)
>  ssize_t elv_iosched_store(struct request_queue *q, const char *name,
>  			  size_t count)
>  {
...
> +	strlcpy(elevator_name, skip_spaces(name),
> sizeof(elevator_name));
> +	strstrip(elevator_name);
> +	ret =3D __elevator_change(q, elevator_name);
>  	if (!ret)
>  		return count;
>=20
> -	printk(KERN_ERR "elevator: switch to %s failed\n", name);
> +	printk(KERN_ERR "elevator: switch to %s failed\n",
> elevator_name);
>  	return ret;
>  }

That leaves two lines of error prints for a single error, and
the second line doesn't convey additional information.

Re: [PATCH] block: Remove leading whitespace and trailing newline in elevator switch error message

[Jens Axboe]

> On May 8, 2017, at 8:18 PM, Elliott, Robert (Persistent Memory) <elliott@h=
pe.com> wrote:
>=20
>=20
>=20
>> -----Original Message-----
>> From: linux-block-owner@vger.kernel.org [mailto:linux-block-
>> owner@vger.kernel.org] On Behalf Of markus@trippelsdorf.de
>> Sent: Saturday, May 06, 2017 12:23 AM
>> To: Bart Van Assche <Bart.VanAssche@sandisk.com>
>> Cc: linux-block@vger.kernel.org; axboe@kernel.dk
>> Subject: [PATCH] block: Remove leading whitespace and trailing
>> newline in elevator switch error message
>>=20
>>=20
>> Trying to switch to a non-existing elevator currently results in
>> garbled
>> dmesg output, e.g.:
>>=20
>> # echo "  foo" > /sys/block/sda/queue/scheduler
>>=20
>> elevator: type   foo not found
>> elevator: switch to   foo
>> failed
> ...
>> @@ -1063,15 +1062,14 @@ static int __elevator_change(struct
>> request_queue *q, const char *name)
>>    if (q->mq_ops && !strncmp(name, "none", 4))
>>        return elevator_switch(q, NULL);
>>=20
>> -    strlcpy(elevator_name, name, sizeof(elevator_name));
>> -    e =3D elevator_get(strstrip(elevator_name), true);
>> +    e =3D elevator_get(name, true);
>>    if (!e) {
>> -        printk(KERN_ERR "elevator: type %s not found\n",
>> elevator_name);
>> +        printk(KERN_ERR "elevator: type %s not found\n", name);
>>        return -EINVAL;
>>    }
> ...
>> @@ -1112,16 +1110,19 @@ static inline bool elv_support_iosched(struct
>> request_queue *q)
>> ssize_t elv_iosched_store(struct request_queue *q, const char *name,
>>              size_t count)
>> {
> ...
>> +    strlcpy(elevator_name, skip_spaces(name),
>> sizeof(elevator_name));
>> +    strstrip(elevator_name);
>> +    ret =3D __elevator_change(q, elevator_name);
>>    if (!ret)
>>        return count;
>>=20
>> -    printk(KERN_ERR "elevator: switch to %s failed\n", name);
>> +    printk(KERN_ERR "elevator: switch to %s failed\n",
>> elevator_name);
>>    return ret;
>> }
>=20
> That leaves two lines of error prints for a single error, and
> the second line doesn't convey additional information.

Yeah good point. Honestly I think we should just kill both lines. None of th=
em add value.=20

Re: [PATCH] block: Remove leading whitespace and trailing newline in elevator switch error message

[markus]

On 2017.05.08 at 20:22 -0600, Jens Axboe wrote:
> 
> > On May 8, 2017, at 8:18 PM, Elliott, Robert (Persistent Memory)
> > <elliott@hpe.com> wrote:
> >> +        printk(KERN_ERR "elevator: type %s not found\n", name);
> > ...
> >> +    printk(KERN_ERR "elevator: switch to %s failed\n",
> > 
> > That leaves two lines of error prints for a single error, and
> > the second line doesn't convey additional information.
> 
> Yeah good point. Honestly I think we should just kill both lines. None
> of them add value. 

They at least help debugging of udev rules, e.g. on Gentoo they have:

 # set noop on solid state drives
 SUBSYSTEM=="block", ACTION=="add", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="noop"

And this will of course fail for mq. But how will you notice it without
any dmesg error message?

-- 
Markus

Re: [PATCH] block: Remove leading whitespace and trailing newline in elevator switch error message

[Jens Axboe]

On 05/08/2017 10:42 PM, markus@trippelsdorf.de wrote:
> On 2017.05.08 at 20:22 -0600, Jens Axboe wrote:
>>
>>> On May 8, 2017, at 8:18 PM, Elliott, Robert (Persistent Memory)
>>> <elliott@hpe.com> wrote:
>>>> +        printk(KERN_ERR "elevator: type %s not found\n", name);
>>> ...
>>>> +    printk(KERN_ERR "elevator: switch to %s failed\n",
>>>
>>> That leaves two lines of error prints for a single error, and
>>> the second line doesn't convey additional information.
>>
>> Yeah good point. Honestly I think we should just kill both lines. None
>> of them add value. 
> 
> They at least help debugging of udev rules, e.g. on Gentoo they have:
> 
>  # set noop on solid state drives
>  SUBSYSTEM=="block", ACTION=="add", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="noop"
> 
> And this will of course fail for mq. But how will you notice it without
> any dmesg error message?

The echo to the sysfs file fails. udev should report such failures. Using
dmesg as the channel to report and discover errors like that is not a
great idea, and it was a mistake to put that code in the switch path
in the first place.

-- 
Jens Axboe