Re: [Xen-devel] [PATCH] libxl: fix transaction leak in logdirty error path

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2012-07-24 at 17:01 +0100, Ian Jackson wrote:
> libxl__domain_suspend_common_switch_qemu_logdirty would leak t if
> there was an error.  Fix this.
> 
> Also, document the intended usage for libxl__xs_transaction_* in the
> doc comment in libxl_internal.h.
> 
> Reported-by: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
> Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

> 
> ---
>  tools/libxl/libxl_dom.c      |    1 +
>  tools/libxl/libxl_internal.h |   36 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 37 insertions(+), 0 deletions(-)
> 
> diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
> index b6111ad..b8a4aae 100644
> --- a/tools/libxl/libxl_dom.c
> +++ b/tools/libxl/libxl_dom.c
> @@ -627,6 +627,7 @@ void libxl__domain_suspend_common_switch_qemu_logdirty
>  
>   out:
>      LOG(ERROR,"logdirty switch failed (rc=%d), aborting suspend",rc);
> +    libxl__xs_transaction_abort(gc, &t);
>      switch_logdirty_done(egc,dss,-1);
>  }
>  
> diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
> index e938660..43bb69b 100644
> --- a/tools/libxl/libxl_internal.h
> +++ b/tools/libxl/libxl_internal.h
> @@ -543,6 +543,42 @@ int libxl__xs_rm_checked(libxl__gc *gc, xs_transaction_t 
> t, const char *path);
>   *   +1  commit conflict; transaction has been destroyed and caller
>   *        must go round again (call _start again and retry)
>   *    0  committed successfully
> + *
> + * The intended usage pattern looks like this:
> + *    int some_function()
> + *    {
> + *        int rc;
> + *        xs_transaction_t t = 0;
> + *        // other initialisations
> + *    
> + *        // do whatever you need to do before the xenstore stuff
> + *        // errors?  set rc and goto out.
> + *    
> + *        for (;;) {
> + *            rc = libxl__xs_transaction_start(gc, &t);
> + *            if (rc) goto out;
> + *    
> + *            // do your work here, including all xenstore reads and writes
> + *            // libxl__xs_*_checked are useful; pass them t.
> + *            // errors?  set rc and goto out.
> + *    
> + *            rc = libxl__xs_transaction_commit(gc, &t);
> + *            if (!rc) break;
> + *            if (rc<0) goto out;
> + *        }
> + *    
> + *        // now the xenstore transaction succeeded
> + *        // do whatever else you need to do
> + *        // errors?  set rc and goto out.
> + *    
> + *        return something;
> + *    
> + *     out:
> + *        // other cleanups
> + *        libxl__xs_transaction_abort(gc, &t);
> + *        // other cleanups
> + *        return rc;
> + *    }
>   */
>  int libxl__xs_transaction_start(libxl__gc *gc, xs_transaction_t *t);
>  int libxl__xs_transaction_commit(libxl__gc *gc, xs_transaction_t *t);



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