[2/2] hw/9pfs: fix alignment issue when host filesystem block size is larger than client msize
diff mbox

Message ID 56C02E4F.6030303@gmail.com
State New
Headers show

Commit Message

Jevon Qiao Feb. 14, 2016, 7:35 a.m. UTC
The following patch is to fix alignment issue when host filesystem block 
size
is larger than client msize.

Thanks,
Jevon

From: Jevon Qiao <scaleqiao@gmail.com>
Date: Sun, 14 Feb 2016 15:11:08 +0800
Subject: [PATCH] hw/9pfs: fix alignment issue when host filesystem block 
size
  is larger than client msize.

Per the previous implementation, iounit will be assigned to be 0 after the
first if statement as (s->msize - P9_IOHDRSZ)/stbuf.f_bsize will be zero 
when
host filesystem block size is larger than msize. Finally, iounit will be 
equal
to s->msize - P9_IOHDRSZ, which is usually not aligned.

Signed-off-by: Jevon Qiao <scaleqiao@gmail.com>
---
  hw/9pfs/virtio-9p.c | 19 ++++++++++++++++---
  1 file changed, 16 insertions(+), 3 deletions(-)

          iounit = s->msize - P9_IOHDRSZ;

Comments

Aneesh Kumar K.V Feb. 14, 2016, 1:38 p.m. UTC | #1
Jevon Qiao <scaleqiao@gmail.com> writes:

> The following patch is to fix alignment issue when host filesystem block 
> size
> is larger than client msize.
>
> Thanks,
> Jevon

That is not the right format to send patch. You can send them as a
series using git-send-email.

>
> From: Jevon Qiao <scaleqiao@gmail.com>
> Date: Sun, 14 Feb 2016 15:11:08 +0800
> Subject: [PATCH] hw/9pfs: fix alignment issue when host filesystem block 
> size
>   is larger than client msize.
>
> Per the previous implementation, iounit will be assigned to be 0 after the
> first if statement as (s->msize - P9_IOHDRSZ)/stbuf.f_bsize will be zero 
> when
> host filesystem block size is larger than msize. Finally, iounit will be 
> equal
> to s->msize - P9_IOHDRSZ, which is usually not aligned.
>
> Signed-off-by: Jevon Qiao <scaleqiao@gmail.com>
> ---
>   hw/9pfs/virtio-9p.c | 19 ++++++++++++++++---
>   1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
> index f972731..005d3a8 100644
> --- a/hw/9pfs/virtio-9p.c
> +++ b/hw/9pfs/virtio-9p.c
> @@ -1326,7 +1326,7 @@ out_nofid:
>   static int32_t get_iounit(V9fsPDU *pdu, V9fsPath *path)
>   {
>       struct statfs stbuf;
> -    int32_t iounit = 0;
> +    int32_t iounit = 0, unit = 0;
>       V9fsState *s = pdu->s;
>
>       /*
> @@ -1334,8 +1334,21 @@ static int32_t get_iounit(V9fsPDU *pdu, V9fsPath 
> *path)
>        * and as well as less than (client msize - P9_IOHDRSZ))
>        */
>       if (!v9fs_co_statfs(pdu, path, &stbuf)) {
> -        iounit = stbuf.f_bsize;
> -        iounit *= (s->msize - P9_IOHDRSZ)/stbuf.f_bsize;
> +    /*
> +     * If host filesystem block size is larger than client msize,
> +     * we will use PAGESIZE as the unit. The reason why we choose
> +     * PAGESIZE is because the data will be splitted in terms of
> +     * PAGESIZE in the virtio layer. In this case, the final
> +     * iounit is equal to the value of ((msize/unit) - 1) * unit.
> +     */
> +    if (stbuf.f_bsize > s->msize) {
> +        iounit = 4096;
> +        unit = 4096;

What page size it should be guest or host ?. Also why 4096 ?. ppc64 use
64K page size.


> +    } else {
> +            iounit = stbuf.f_bsize;
> +        unit = stbuf.f_bsize;
> +    }
> +        iounit *= (s->msize - P9_IOHDRSZ)/unit;
>       }
>       if (!iounit) {
>           iounit = s->msize - P9_IOHDRSZ;
> -- 

-aneesh

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Jevon Qiao Feb. 17, 2016, 7:14 a.m. UTC | #2
Hi Aneesh,

Thank you for reviewing my code, please see my reply in-line.
On 14/2/16 21:38, Aneesh Kumar K.V wrote:
> Jevon Qiao <scaleqiao@gmail.com> writes:
>
>> The following patch is to fix alignment issue when host filesystem block
>> size
>> is larger than client msize.
>>
>> Thanks,
>> Jevon
> That is not the right format to send patch. You can send them as a
> series using git-send-email.
Yes, you're correct. I will send the patches later after I address all 
the technical comments.
>> From: Jevon Qiao <scaleqiao@gmail.com>
>> Date: Sun, 14 Feb 2016 15:11:08 +0800
>> Subject: [PATCH] hw/9pfs: fix alignment issue when host filesystem block
>> size
>>    is larger than client msize.
>>
>> Per the previous implementation, iounit will be assigned to be 0 after the
>> first if statement as (s->msize - P9_IOHDRSZ)/stbuf.f_bsize will be zero
>> when
>> host filesystem block size is larger than msize. Finally, iounit will be
>> equal
>> to s->msize - P9_IOHDRSZ, which is usually not aligned.
>>
>> Signed-off-by: Jevon Qiao <scaleqiao@gmail.com>
>> ---
>>    hw/9pfs/virtio-9p.c | 19 ++++++++++++++++---
>>    1 file changed, 16 insertions(+), 3 deletions(-)
>>
>> diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
>> index f972731..005d3a8 100644
>> --- a/hw/9pfs/virtio-9p.c
>> +++ b/hw/9pfs/virtio-9p.c
>> @@ -1326,7 +1326,7 @@ out_nofid:
>>    static int32_t get_iounit(V9fsPDU *pdu, V9fsPath *path)
>>    {
>>        struct statfs stbuf;
>> -    int32_t iounit = 0;
>> +    int32_t iounit = 0, unit = 0;
>>        V9fsState *s = pdu->s;
>>
>>        /*
>> @@ -1334,8 +1334,21 @@ static int32_t get_iounit(V9fsPDU *pdu, V9fsPath
>> *path)
>>         * and as well as less than (client msize - P9_IOHDRSZ))
>>         */
>>        if (!v9fs_co_statfs(pdu, path, &stbuf)) {
>> -        iounit = stbuf.f_bsize;
>> -        iounit *= (s->msize - P9_IOHDRSZ)/stbuf.f_bsize;
>> +    /*
>> +     * If host filesystem block size is larger than client msize,
>> +     * we will use PAGESIZE as the unit. The reason why we choose
>> +     * PAGESIZE is because the data will be splitted in terms of
>> +     * PAGESIZE in the virtio layer. In this case, the final
>> +     * iounit is equal to the value of ((msize/unit) - 1) * unit.
>> +     */
>> +    if (stbuf.f_bsize > s->msize) {
>> +        iounit = 4096;
>> +        unit = 4096;
> What page size it should be guest or host ?. Also why 4096 ?. ppc64 use
> 64K page size.
The data to be read or written will be divided into pieces according to the
size of iounit and msize firstly, and then mapped to pages before being 
added
into virtqueue. Since all these operations happen in the guest side, so the
page size should be guest. Please correct me if I'm wrong.

As for the number 4096, It's the default value in Linux OS. I did not take
other platforms into account, it's my fault. To make it suitable for all 
platforms,
shall I use the function getpagesize() here?

Thanks,
Jevon
>> +    } else {
>> +            iounit = stbuf.f_bsize;
>> +        unit = stbuf.f_bsize;
>> +    }
>> +        iounit *= (s->msize - P9_IOHDRSZ)/unit;
>>        }
>>        if (!iounit) {
>>            iounit = s->msize - P9_IOHDRSZ;
>> -- 
> -aneesh
>

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Greg Kurz Feb. 17, 2016, 10:24 a.m. UTC | #3
On Wed, 17 Feb 2016 15:14:48 +0800
Jevon Qiao <scaleqiao@gmail.com> wrote:

> Hi Aneesh,
> 
> Thank you for reviewing my code, please see my reply in-line.

Jevon,

Please read comments below.

> On 14/2/16 21:38, Aneesh Kumar K.V wrote:
> > Jevon Qiao <scaleqiao@gmail.com> writes:
> >  
> >> The following patch is to fix alignment issue when host filesystem block
> >> size
> >> is larger than client msize.
> >>
> >> Thanks,
> >> Jevon  
> > That is not the right format to send patch. You can send them as a
> > series using git-send-email.  
> Yes, you're correct. I will send the patches later after I address all 
> the technical comments.
> >> From: Jevon Qiao <scaleqiao@gmail.com>
> >> Date: Sun, 14 Feb 2016 15:11:08 +0800
> >> Subject: [PATCH] hw/9pfs: fix alignment issue when host filesystem block
> >> size
> >>    is larger than client msize.
> >>
> >> Per the previous implementation, iounit will be assigned to be 0 after the
> >> first if statement as (s->msize - P9_IOHDRSZ)/stbuf.f_bsize will be zero
> >> when
> >> host filesystem block size is larger than msize. Finally, iounit will be
> >> equal
> >> to s->msize - P9_IOHDRSZ, which is usually not aligned.
> >>
> >> Signed-off-by: Jevon Qiao <scaleqiao@gmail.com>
> >> ---
> >>    hw/9pfs/virtio-9p.c | 19 ++++++++++++++++---

Hmmm I just realize your tree is not up-to-date since hw/9pfs/virtio-9p.c got
renamed with this recent commit:

commit 60ce86c7140d5ca33d5fd87ce821681165d06b2a
Author: Wei Liu <wei.liu2@citrix.com>
Date:   Thu Jan 7 18:42:20 2016 +0000

    9pfs: rename virtio-9p.c to 9p.c

Also 9p.c only contains generic code now, not related to virtio... see below.

> >>    1 file changed, 16 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
> >> index f972731..005d3a8 100644
> >> --- a/hw/9pfs/virtio-9p.c
> >> +++ b/hw/9pfs/virtio-9p.c
> >> @@ -1326,7 +1326,7 @@ out_nofid:
> >>    static int32_t get_iounit(V9fsPDU *pdu, V9fsPath *path)
> >>    {
> >>        struct statfs stbuf;
> >> -    int32_t iounit = 0;
> >> +    int32_t iounit = 0, unit = 0;
> >>        V9fsState *s = pdu->s;
> >>
> >>        /*
> >> @@ -1334,8 +1334,21 @@ static int32_t get_iounit(V9fsPDU *pdu, V9fsPath
> >> *path)
> >>         * and as well as less than (client msize - P9_IOHDRSZ))
> >>         */
> >>        if (!v9fs_co_statfs(pdu, path, &stbuf)) {
> >> -        iounit = stbuf.f_bsize;
> >> -        iounit *= (s->msize - P9_IOHDRSZ)/stbuf.f_bsize;
> >> +    /*
> >> +     * If host filesystem block size is larger than client msize,
> >> +     * we will use PAGESIZE as the unit. The reason why we choose
> >> +     * PAGESIZE is because the data will be splitted in terms of
> >> +     * PAGESIZE in the virtio layer. In this case, the final

... and here you mention virtio. Does this code really belong here ?

> >> +     * iounit is equal to the value of ((msize/unit) - 1) * unit.
> >> +     */
> >> +    if (stbuf.f_bsize > s->msize) {
> >> +        iounit = 4096;
> >> +        unit = 4096;  

This looks weird when reading the initial comment in get_iounit()... is
iounit a multiple of stbuf.f_bsize in this case ?

> > What page size it should be guest or host ?. Also why 4096 ?. ppc64 use
> > 64K page size.  
> The data to be read or written will be divided into pieces according to the
> size of iounit and msize firstly, and then mapped to pages before being 
> added
> into virtqueue. Since all these operations happen in the guest side, so the
> page size should be guest. Please correct me if I'm wrong.
> 
> As for the number 4096, It's the default value in Linux OS. I did not take
> other platforms into account, it's my fault. To make it suitable for all 
> platforms,
> shall I use the function getpagesize() here?
> 

getpagesize() will return the host page size. If you need the guest page size,
you should use TARGET_PAGE_SIZE.

And then you will hit another problem: the 9p.c file is in common-obj and
cannot contain target specific code...

Along with the other remark, I'm beginning to think you may need to move this
to virtio-9p-device.c.

> Thanks,
> Jevon
> >> +    } else {
> >> +            iounit = stbuf.f_bsize;
> >> +        unit = stbuf.f_bsize;
> >> +    }
> >> +        iounit *= (s->msize - P9_IOHDRSZ)/unit;
> >>        }
> >>        if (!iounit) {
> >>            iounit = s->msize - P9_IOHDRSZ;
> >> --   
> > -aneesh
> >  
> 

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Aneesh Kumar K.V Feb. 17, 2016, 2:44 p.m. UTC | #4
Jevon Qiao <scaleqiao@gmail.com> writes:

> Hi Aneesh,
>
> Thank you for reviewing my code, please see my reply in-line.
> On 14/2/16 21:38, Aneesh Kumar K.V wrote:
>> Jevon Qiao <scaleqiao@gmail.com> writes:
>>
>>> The following patch is to fix alignment issue when host filesystem block
>>> size
>>> is larger than client msize.
>>>
>>> Thanks,
>>> Jevon
>> That is not the right format to send patch. You can send them as a
>> series using git-send-email.
> Yes, you're correct. I will send the patches later after I address all 
> the technical comments.
>>> From: Jevon Qiao <scaleqiao@gmail.com>
>>> Date: Sun, 14 Feb 2016 15:11:08 +0800
>>> Subject: [PATCH] hw/9pfs: fix alignment issue when host filesystem block
>>> size
>>>    is larger than client msize.
>>>
>>> Per the previous implementation, iounit will be assigned to be 0 after the
>>> first if statement as (s->msize - P9_IOHDRSZ)/stbuf.f_bsize will be zero
>>> when
>>> host filesystem block size is larger than msize. Finally, iounit will be
>>> equal
>>> to s->msize - P9_IOHDRSZ, which is usually not aligned.
>>>
>>> Signed-off-by: Jevon Qiao <scaleqiao@gmail.com>
>>> ---
>>>    hw/9pfs/virtio-9p.c | 19 ++++++++++++++++---
>>>    1 file changed, 16 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
>>> index f972731..005d3a8 100644
>>> --- a/hw/9pfs/virtio-9p.c
>>> +++ b/hw/9pfs/virtio-9p.c
>>> @@ -1326,7 +1326,7 @@ out_nofid:
>>>    static int32_t get_iounit(V9fsPDU *pdu, V9fsPath *path)
>>>    {
>>>        struct statfs stbuf;
>>> -    int32_t iounit = 0;
>>> +    int32_t iounit = 0, unit = 0;
>>>        V9fsState *s = pdu->s;
>>>
>>>        /*
>>> @@ -1334,8 +1334,21 @@ static int32_t get_iounit(V9fsPDU *pdu, V9fsPath
>>> *path)
>>>         * and as well as less than (client msize - P9_IOHDRSZ))
>>>         */
>>>        if (!v9fs_co_statfs(pdu, path, &stbuf)) {
>>> -        iounit = stbuf.f_bsize;
>>> -        iounit *= (s->msize - P9_IOHDRSZ)/stbuf.f_bsize;
>>> +    /*
>>> +     * If host filesystem block size is larger than client msize,
>>> +     * we will use PAGESIZE as the unit. The reason why we choose
>>> +     * PAGESIZE is because the data will be splitted in terms of
>>> +     * PAGESIZE in the virtio layer. In this case, the final
>>> +     * iounit is equal to the value of ((msize/unit) - 1) * unit.
>>> +     */
>>> +    if (stbuf.f_bsize > s->msize) {
>>> +        iounit = 4096;
>>> +        unit = 4096;
>> What page size it should be guest or host ?. Also why 4096 ?. ppc64 use
>> 64K page size.
> The data to be read or written will be divided into pieces according to the
> size of iounit and msize firstly, and then mapped to pages before being 
> added
> into virtqueue. Since all these operations happen in the guest side, so the
> page size should be guest. Please correct me if I'm wrong.

I am not sure I understand the details correctly. iounit is the size
that we use in client_read to determine the  size in which
we should request I/O from the client. But we still can't do I/O in size
larger than s->msize. If you look at the client side (kernel 9p fs), you
will find

	rsize = fid->iounit;
	if (!rsize || rsize > clnt->msize-P9_IOHDRSZ)
		rsize = clnt->msize - P9_IOHDRSZ;

if your iounit calculation ends up zero, that should be handled
correctly by

    if (!iounit) {
        iounit = s->msize - P9_IOHDRSZ;
    }
    return iounit;


So what is the issue here. ?

-aneesh

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Jevon Qiao Feb. 19, 2016, 9:32 a.m. UTC | #5
Hi Greg,
>>>> From: Jevon Qiao <scaleqiao@gmail.com>
>>>> Date: Sun, 14 Feb 2016 15:11:08 +0800
>>>> Subject: [PATCH] hw/9pfs: fix alignment issue when host filesystem block
>>>> size
>>>>     is larger than client msize.
>>>>
>>>> Per the previous implementation, iounit will be assigned to be 0 after the
>>>> first if statement as (s->msize - P9_IOHDRSZ)/stbuf.f_bsize will be zero
>>>> when
>>>> host filesystem block size is larger than msize. Finally, iounit will be
>>>> equal
>>>> to s->msize - P9_IOHDRSZ, which is usually not aligned.
>>>>
>>>> Signed-off-by: Jevon Qiao <scaleqiao@gmail.com>
>>>> ---
>>>>     hw/9pfs/virtio-9p.c | 19 ++++++++++++++++---
> Hmmm I just realize your tree is not up-to-date since hw/9pfs/virtio-9p.c got
> renamed with this recent commit:
>
> commit 60ce86c7140d5ca33d5fd87ce821681165d06b2a
> Author: Wei Liu <wei.liu2@citrix.com>
> Date:   Thu Jan 7 18:42:20 2016 +0000
>
>      9pfs: rename virtio-9p.c to 9p.c
>
> Also 9p.c only contains generic code now, not related to virtio... see below.
The feature was finished before it happened, I'm sorry I did not sync my 
tree up
with master.
>>>>     1 file changed, 16 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
>>>> index f972731..005d3a8 100644
>>>> --- a/hw/9pfs/virtio-9p.c
>>>> +++ b/hw/9pfs/virtio-9p.c
>>>> @@ -1326,7 +1326,7 @@ out_nofid:
>>>>     static int32_t get_iounit(V9fsPDU *pdu, V9fsPath *path)
>>>>     {
>>>>         struct statfs stbuf;
>>>> -    int32_t iounit = 0;
>>>> +    int32_t iounit = 0, unit = 0;
>>>>         V9fsState *s = pdu->s;
>>>>
>>>>         /*
>>>> @@ -1334,8 +1334,21 @@ static int32_t get_iounit(V9fsPDU *pdu, V9fsPath
>>>> *path)
>>>>          * and as well as less than (client msize - P9_IOHDRSZ))
>>>>          */
>>>>         if (!v9fs_co_statfs(pdu, path, &stbuf)) {
>>>> -        iounit = stbuf.f_bsize;
>>>> -        iounit *= (s->msize - P9_IOHDRSZ)/stbuf.f_bsize;
>>>> +    /*
>>>> +     * If host filesystem block size is larger than client msize,
>>>> +     * we will use PAGESIZE as the unit. The reason why we choose
>>>> +     * PAGESIZE is because the data will be splitted in terms of
>>>> +     * PAGESIZE in the virtio layer. In this case, the final
> ... and here you mention virtio. Does this code really belong here ?
Sorry for confusing you, the comment might not be very clear. Here I mean
the issue I mentioned in another thread with Aneesh. It's not related to 
virtio.
>>>> +     * iounit is equal to the value of ((msize/unit) - 1) * unit.
>>>> +     */
>>>> +    if (stbuf.f_bsize > s->msize) {
>>>> +        iounit = 4096;
>>>> +        unit = 4096;
> This looks weird when reading the initial comment in get_iounit()... is
> iounit a multiple of stbuf.f_bsize in this case ?
Yes, I think so. The stbuf.f_bsize refers to the iounit of backend 
filesystem,
and to comply with the backend is a right way to go always.
>>> What page size it should be guest or host ?. Also why 4096 ?. ppc64 use
>>> 64K page size.
>> The data to be read or written will be divided into pieces according to the
>> size of iounit and msize firstly, and then mapped to pages before being
>> added
>> into virtqueue. Since all these operations happen in the guest side, so the
>> page size should be guest. Please correct me if I'm wrong.
>>
>> As for the number 4096, It's the default value in Linux OS. I did not take
>> other platforms into account, it's my fault. To make it suitable for all
>> platforms,
>> shall I use the function getpagesize() here?
>>
> getpagesize() will return the host page size. If you need the guest page size,
> you should use TARGET_PAGE_SIZE.
> And then you will hit another problem: the 9p.c file is in common-obj and
> cannot contain target specific code...
Well, good to know this, thank you for sharing this.
> Along with the other remark, I'm beginning to think you may need to move this
> to virtio-9p-device.c.
I'll think of this, thank you for the option.

Thanks,
Jevon
>> Thanks,
>> Jevon
>>>> +    } else {
>>>> +            iounit = stbuf.f_bsize;
>>>> +        unit = stbuf.f_bsize;
>>>> +    }
>>>> +        iounit *= (s->msize - P9_IOHDRSZ)/unit;
>>>>         }
>>>>         if (!iounit) {
>>>>             iounit = s->msize - P9_IOHDRSZ;
>>>> --
>>> -aneesh
>>>   

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Patch
diff mbox

diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
index f972731..005d3a8 100644
--- a/hw/9pfs/virtio-9p.c
+++ b/hw/9pfs/virtio-9p.c
@@ -1326,7 +1326,7 @@  out_nofid:
  static int32_t get_iounit(V9fsPDU *pdu, V9fsPath *path)
  {
      struct statfs stbuf;
-    int32_t iounit = 0;
+    int32_t iounit = 0, unit = 0;
      V9fsState *s = pdu->s;

      /*
@@ -1334,8 +1334,21 @@  static int32_t get_iounit(V9fsPDU *pdu, V9fsPath 
*path)
       * and as well as less than (client msize - P9_IOHDRSZ))
       */
      if (!v9fs_co_statfs(pdu, path, &stbuf)) {
-        iounit = stbuf.f_bsize;
-        iounit *= (s->msize - P9_IOHDRSZ)/stbuf.f_bsize;
+    /*
+     * If host filesystem block size is larger than client msize,
+     * we will use PAGESIZE as the unit. The reason why we choose
+     * PAGESIZE is because the data will be splitted in terms of
+     * PAGESIZE in the virtio layer. In this case, the final
+     * iounit is equal to the value of ((msize/unit) - 1) * unit.
+     */
+    if (stbuf.f_bsize > s->msize) {
+        iounit = 4096;
+        unit = 4096;
+    } else {
+            iounit = stbuf.f_bsize;
+        unit = stbuf.f_bsize;
+    }
+        iounit *= (s->msize - P9_IOHDRSZ)/unit;
      }
      if (!iounit) {