Re: [Qemu-devel] [PATCH v2 2/2] Replace rwlocks with RCU variants of interfaces.

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

On Fri, 14 Oct 2011 02:05:02 +0530, Harsh Prateek Bora <harsh@linux.vnet.ibm.com> wrote:
> Use QLIST_INSERT_HEAD_RCU and rcu_read_lock/unlock instead of rwlocks.
> Use v9fs_synth_mutex as a write-only mutex to handle concurrent writers.
> 
> Signed-off-by: Harsh Prateek Bora <harsh@linux.vnet.ibm.com>
> ---
>  hw/9pfs/virtio-9p-synth.c |   26 ++++++++++++--------------
>  1 files changed, 12 insertions(+), 14 deletions(-)
> 
> diff --git a/hw/9pfs/virtio-9p-synth.c b/hw/9pfs/virtio-9p-synth.c
> index cbf74e4..567611e 100644
> --- a/hw/9pfs/virtio-9p-synth.c
> +++ b/hw/9pfs/virtio-9p-synth.c
> @@ -30,8 +30,7 @@ V9fsSynthNode v9fs_synth_root = {
>      .attr = &v9fs_synth_root.actual_attr,
>  };
> 
> -/*FIXME!! should be converted to qemu_rwlock_t */
> -static pthread_rwlock_t v9fs_synth_mutex;
> +static QemuMutex  v9fs_synth_mutex;
>  static int v9fs_synth_node_count;
>  /* set to 1 when the synth fs is ready */
>  static int v9fs_synth_fs;
> @@ -79,7 +78,7 @@ int qemu_v9fs_synth_mkdir(V9fsSynthNode *parent, int mode,
>      if (!parent) {
>          parent = &v9fs_synth_root;
>      }
> -    pthread_rwlock_wrlock(&v9fs_synth_mutex);
> +    qemu_mutex_lock(&v9fs_synth_mutex);
>      QLIST_FOREACH(tmp, &parent->child, sibling) {
>          if (!strcmp(tmp->name, name)) {
>              ret = EEXIST;
> @@ -95,7 +94,7 @@ int qemu_v9fs_synth_mkdir(V9fsSynthNode *parent, int mode,
>      *result = node;
>      ret = 0;
>  err_out:
> -    pthread_rwlock_unlock(&v9fs_synth_mutex);
> +    qemu_mutex_unlock(&v9fs_synth_mutex);
>      return ret;


We sould be using QLIST_INSERT_HEAD_RCU even in v9fs_add_dir_node


>  }
> 
> @@ -116,7 +115,7 @@ int qemu_v9fs_synth_add_file(V9fsSynthNode *parent, int mode,
>          parent = &v9fs_synth_root;
>      }
> 

-aneesh