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Date: Mon, 14 Nov 2016 18:32:26 +0100
From: Greg Kurz <groug@kaod.org>
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Subject: Re: [Qemu-devel] [PATCH 1/3] 9pfs: add cleanup operation in
 FileOperations
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To: Li Qiang <liq3ea@gmail.com>
Cc: qemu-devel@nongnu.org, liqiang6-s@360.cn

On Mon, 14 Nov 2016 07:32:56 -0500
Li Qiang <liq3ea@gmail.com> wrote:

> From: Li Qiang <liq3ea@gmail.com>
> 
> Currently, the backend of VirtFS doesn't have a cleanup
> function. This will lead resource leak issues if the backed
> driver allocates resources. This patch addresses this issue.
> 
> Signed-off-by: Li Qiang <liq3ea@gmail.com>
> ---
>  fsdev/file-op-9p.h | 1 +
>  hw/9pfs/9p.c       | 3 +++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/fsdev/file-op-9p.h b/fsdev/file-op-9p.h
> index 6db9fea..a56dc84 100644
> --- a/fsdev/file-op-9p.h
> +++ b/fsdev/file-op-9p.h
> @@ -100,6 +100,7 @@ struct FileOperations
>  {
>      int (*parse_opts)(QemuOpts *, struct FsDriverEntry *);
>      int (*init)(struct FsContext *);
> +    void (*cleanup)(struct FsContext *);
>      int (*lstat)(FsContext *, V9fsPath *, struct stat *);
>      ssize_t (*readlink)(FsContext *, V9fsPath *, char *, size_t);
>      int (*chmod)(FsContext *, V9fsPath *, FsCred *);
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index aea7e9d..166b5a7 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -3532,6 +3532,9 @@ void v9fs_device_unrealize_common(V9fsState *s, Error **errp)
>  {
>      g_free(s->ctx.fs_root);
>      g_free(s->tag);
> +    if (s->ops->cleanup) {
> +        s->ops->cleanup(&s->ctx);
> +    }

Unrealize should undo things that were set during realize in reverse order: 
please move the cleanup stuff above calls to g_free() (which are actually
misordered since tag is allocated after fs_root... maybe you can fix that
too in a preparatory patch).

You also have to call cleanup in the error path of realize if init was
called.

>  }
>  
>  typedef struct VirtfsCoResetData {