Re: [Qemu-devel] [V2 06/25] [virtio-9p] coroutines for readlink

[Stefan Hajnoczi <stefanha@gmail.com>]

On Thu, May 19, 2011 at 4:28 PM, Venkateswararao Jujjuri
<jvrao@linux.vnet.ibm.com> wrote:
> On 05/18/2011 10:37 PM, Stefan Hajnoczi wrote:
>>
>> On Wed, May 18, 2011 at 7:42 PM, Venkateswararao Jujjuri
>> <jvrao@linux.vnet.ibm.com>  wrote:
>>>
>>> On 05/18/2011 02:43 AM, Stefan Hajnoczi wrote:
>>>>
>>>> On Tue, May 17, 2011 at 8:43 PM, Venkateswararao Jujjuri (JV)
>>>> <jvrao@linux.vnet.ibm.com>    wrote:
>>>>>
>>>>> Signed-off-by: Venkateswararao Jujjuri "<jvrao@linux.vnet.ibm.com>
>>>>> ---
>>>>>  Makefile.objs            |    2 +-
>>>>>  hw/9pfs/cofs.c           |   42
>>>>> ++++++++++++++++++++++++++++++++++++++++++
>>>>>  hw/9pfs/virtio-9p-coth.h |    1 +
>>>>>  hw/9pfs/virtio-9p.c      |   27 ++++-----------------------
>>>>>  hw/9pfs/virtio-9p.h      |    3 ++-
>>>>>  5 files changed, 50 insertions(+), 25 deletions(-)
>>>>>  create mode 100644 hw/9pfs/cofs.c
>>>>>
>>>>> diff --git a/Makefile.objs b/Makefile.objs
>>>>> index 96f6a24..36005bb 100644
>>>>> --- a/Makefile.objs
>>>>> +++ b/Makefile.objs
>>>>> @@ -297,7 +297,7 @@ hw-obj-$(CONFIG_SOUND) += $(sound-obj-y)
>>>>>  9pfs-nested-$(CONFIG_VIRTFS) = virtio-9p.o virtio-9p-debug.o
>>>>>  9pfs-nested-$(CONFIG_VIRTFS) +=  virtio-9p-local.o virtio-9p-xattr.o
>>>>>  9pfs-nested-$(CONFIG_VIRTFS) +=   virtio-9p-xattr-user.o
>>>>> virtio-9p-posix-acl.o
>>>>> -9pfs-nested-$(CONFIG_VIRTFS) += virtio-9p-coth.o
>>>>> +9pfs-nested-$(CONFIG_VIRTFS) += virtio-9p-coth.o cofs.o
>>>>>
>>>>>  hw-obj-$(CONFIG_REALLY_VIRTFS) += $(addprefix 9pfs/, $(9pfs-nested-y))
>>>>>  $(addprefix 9pfs/, $(9pfs-nested-y)): QEMU_CFLAGS+=$(GLIB_CFLAGS)
>>>>> diff --git a/hw/9pfs/cofs.c b/hw/9pfs/cofs.c
>>>>> new file mode 100644
>>>>> index 0000000..6d94673
>>>>> --- /dev/null
>>>>> +++ b/hw/9pfs/cofs.c
>>>>> @@ -0,0 +1,42 @@
>>>>> +
>>>>> +/*
>>>>> + * Virtio 9p backend
>>>>> + *
>>>>> + * Copyright IBM, Corp. 2011
>>>>> + *
>>>>> + * Authors:
>>>>> + *  Aneesh Kumar K.V<aneesh.kumar@linux.vnet.ibm.com>
>>>>> + *
>>>>> + * This work is licensed under the terms of the GNU GPL, version 2.
>>>>>  See
>>>>> + * the COPYING file in the top-level directory.
>>>>> + *
>>>>> + */
>>>>> +
>>>>> +#include "fsdev/qemu-fsdev.h"
>>>>> +#include "qemu-thread.h"
>>>>> +#include "qemu-coroutine.h"
>>>>> +#include "virtio-9p-coth.h"
>>>>> +
>>>>> +int v9fs_co_readlink(V9fsState *s, V9fsString *path, V9fsString *buf)
>>>>> +{
>>>>> +    int err;
>>>>> +    ssize_t len;
>>>>> +    V9fsString tbuf;
>>>>> +
>>>>> +    tbuf.data = qemu_malloc(PATH_MAX);
>>>>
>>>> Why introduce tbuf when the buf is available?  You end up having to
>>>> copy back fields at the end of the function and load from an
>>>> uninitialized address (tbuf.size) in the error case.
>>>
>>> tbuf is introduced for re-entrent purpose.
>>> We should be calling v9fs_string_init() on this though.
>>
>> I see no issue here and no safety added by using a local variable.
>> Can you explain what you're trying to do?
>
> No issues in the current usage. Just looking at the micro level of this
> routine,
> we have an passd-in buffer passed under lock and is getting updated outside
> the lock (worker thread).
> Can take it out, not an issue.

Please take it out since it isn't needed.

Stefan