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

[Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>]

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.

- JV

> Stefan
>