Re: [Qemu-devel] [PATCH v2 2/3] error: Remove unnecessary local_err variables

[Eduardo Habkost]

On Mon, Jun 13, 2016 at 01:42:15PM +0200, Markus Armbruster wrote:
> Eduardo Habkost  writes:
> 
> > This patch simplifies code that uses a local_err variable just to
> > immediately use it for an error_propagate() call.
> >
> > Coccinelle patch used to perform the changes added to
> > scripts/coccinelle/remove_local_err.cocci.
> >
> > Signed-off-by: Eduardo Habkost 
> [...]
> > diff --git a/scripts/coccinelle/remove_local_err.cocci 
> > b/scripts/coccinelle/remove_local_err.cocci
> > new file mode 100644
> > index 000..5f0b6c0
> > --- /dev/null
> > +++ b/scripts/coccinelle/remove_local_err.cocci
> > @@ -0,0 +1,27 @@
> > +// Replace unnecessary usage of local_err variable with
> > +// direct usage of errp argument
> > +
> > +@@
> > +expression list ARGS;
> > +expression F2;
> > +identifier LOCAL_ERR;
> > +expression ERRP;
> > +idexpression V;
> > +typedef Error;
> > +expression I;
> 
> I isn't used.
> 
> > +@@
> > + {
> > + ...
> > +-Error *LOCAL_ERR;
> > + ... when != LOCAL_ERR
> > +(
> > +-F2(ARGS, _ERR);
> > +-error_propagate(ERRP, LOCAL_ERR);
> > ++F2(ARGS, ERRP);
> > +|
> > +-V = F2(ARGS, _ERR);
> > +-error_propagate(ERRP, LOCAL_ERR);
> > ++V = F2(ARGS, ERRP);
> > +)
> > + ... when != LOCAL_ERR
> > + }
> 
> There is an (ugly) difference between
> 
> error_setg(_err, ...);
> error_propagate(errp, _err);
> 
> and
> 
> error_setg(errp, ...);
> 
> The latter aborts when @errp already contains an error, the former does
> nothing.

Why the difference? Couldn't we change that so that both are equivalent?

> 
> Your transformation has the error_setg() or similar hidden in F2().  It
> can add aborts.
> 
> I think it can be salvaged: we know that @errp must not contain an error
> on function entry.  If @errp doesn't occur elsewhere in this function,
> it cannot pick up an error on the way to the transformed spot.  Can you
> add that to your when constraints?

Do we really know that *errp is NULL on entry? Aren't we allowed to call
functions with a non-NULL *errp?

See, e.g.:

void qmp_guest_suspend_disk(Error **errp)
{
Error *local_err = NULL;
GuestSuspendMode *mode = g_new(GuestSuspendMode, 1);

*mode = GUEST_SUSPEND_MODE_DISK;
check_suspend_mode(*mode, _err);
acquire_privilege(SE_SHUTDOWN_NAME, _err);
execute_async(do_suspend, mode, _err);

if (local_err) {
error_propagate(errp, local_err);
g_free(mode);
}
}


-- 
Eduardo

Re: [Qemu-devel] [PATCH v2 2/3] error: Remove unnecessary local_err variables

[Markus Armbruster]

Eduardo Habkost  writes:

> This patch simplifies code that uses a local_err variable just to
> immediately use it for an error_propagate() call.
>
> Coccinelle patch used to perform the changes added to
> scripts/coccinelle/remove_local_err.cocci.
>
> Signed-off-by: Eduardo Habkost 
[...]
> diff --git a/scripts/coccinelle/remove_local_err.cocci 
> b/scripts/coccinelle/remove_local_err.cocci
> new file mode 100644
> index 000..5f0b6c0
> --- /dev/null
> +++ b/scripts/coccinelle/remove_local_err.cocci
> @@ -0,0 +1,27 @@
> +// Replace unnecessary usage of local_err variable with
> +// direct usage of errp argument
> +
> +@@
> +expression list ARGS;
> +expression F2;
> +identifier LOCAL_ERR;
> +expression ERRP;
> +idexpression V;
> +typedef Error;
> +expression I;

I isn't used.

> +@@
> + {
> + ...
> +-Error *LOCAL_ERR;
> + ... when != LOCAL_ERR
> +(
> +-F2(ARGS, _ERR);
> +-error_propagate(ERRP, LOCAL_ERR);
> ++F2(ARGS, ERRP);
> +|
> +-V = F2(ARGS, _ERR);
> +-error_propagate(ERRP, LOCAL_ERR);
> ++V = F2(ARGS, ERRP);
> +)
> + ... when != LOCAL_ERR
> + }

There is an (ugly) difference between

error_setg(_err, ...);
error_propagate(errp, _err);

and

error_setg(errp, ...);

The latter aborts when @errp already contains an error, the former does
nothing.

Your transformation has the error_setg() or similar hidden in F2().  It
can add aborts.

I think it can be salvaged: we know that @errp must not contain an error
on function entry.  If @errp doesn't occur elsewhere in this function,
it cannot pick up an error on the way to the transformed spot.  Can you
add that to your when constraints?

[...]

Re: [Qemu-devel] [PATCH v2 2/3] error: Remove unnecessary local_err variables

[Cornelia Huck]

On Fri, 10 Jun 2016 17:12:17 -0300
Eduardo Habkost  wrote:

> This patch simplifies code that uses a local_err variable just to
> immediately use it for an error_propagate() call.
> 
> Coccinelle patch used to perform the changes added to
> scripts/coccinelle/remove_local_err.cocci.
> 
> Signed-off-by: Eduardo Habkost 
> ---
>  block.c   |  8 ++--
>  block/raw-posix.c |  8 ++--
>  block/raw_bsd.c   |  4 +---
>  blockdev.c| 16 +---
>  hw/s390x/s390-virtio-ccw.c|  5 +
>  hw/s390x/virtio-ccw.c | 28 +++-

For the two virtio-ccw files:

Acked-by: Cornelia Huck 

>  scripts/coccinelle/remove_local_err.cocci | 27 +++
>  target-i386/cpu.c |  4 +---
>  8 files changed, 46 insertions(+), 54 deletions(-)
>  create mode 100644 scripts/coccinelle/remove_local_err.cocci

Re: [Qemu-devel] [PATCH v2 2/3] error: Remove unnecessary local_err variables

[Eduardo Habkost]

On Fri, Jun 10, 2016 at 02:59:55PM -0600, Eric Blake wrote:
> On 06/10/2016 02:12 PM, Eduardo Habkost wrote:
> > This patch simplifies code that uses a local_err variable just to
> > immediately use it for an error_propagate() call.
> > 
> > Coccinelle patch used to perform the changes added to
> > scripts/coccinelle/remove_local_err.cocci.
> > 
> > Signed-off-by: Eduardo Habkost 
> > ---
> >  block.c   |  8 ++--
> >  block/raw-posix.c |  8 ++--
> >  block/raw_bsd.c   |  4 +---
> >  blockdev.c| 16 +---
> >  hw/s390x/s390-virtio-ccw.c|  5 +
> >  hw/s390x/virtio-ccw.c | 28 +++-
> >  scripts/coccinelle/remove_local_err.cocci | 27 +++
> >  target-i386/cpu.c |  4 +---
> >  8 files changed, 46 insertions(+), 54 deletions(-)
> >  create mode 100644 scripts/coccinelle/remove_local_err.cocci
> > 
> 
> > +++ b/block.c
> > @@ -294,14 +294,12 @@ typedef struct CreateCo {
> >  
> >  static void coroutine_fn bdrv_create_co_entry(void *opaque)
> >  {
> > -Error *local_err = NULL;
> >  int ret;
> >  
> >  CreateCo *cco = opaque;
> >  assert(cco->drv);
> >  
> > -ret = cco->drv->bdrv_create(cco->filename, cco->opts, _err);
> > -error_propagate(>err, local_err);
> > +ret = cco->drv->bdrv_create(cco->filename, cco->opts, >err);
> >  cco->ret = ret;
> 
> This hunk doesn't get simplified by 3/3; you may want to consider a
> manual followup to drop 'int ret' and just assign
> cco->drv->bdrv_create() directly to cco->ret.  But doesn't change this
> patch.

This could become yet another Coccinelle script, but we need to
be careful about type conversions, and tell it to do it only if
the types of 'ret', 'cc->drv->bdrv_create()' and 'cco->ret' are
the same.

-- 
Eduardo

Re: [Qemu-devel] [PATCH v2 2/3] error: Remove unnecessary local_err variables

[Eric Blake]

On 06/10/2016 02:12 PM, Eduardo Habkost wrote:
> This patch simplifies code that uses a local_err variable just to
> immediately use it for an error_propagate() call.
> 
> Coccinelle patch used to perform the changes added to
> scripts/coccinelle/remove_local_err.cocci.
> 
> Signed-off-by: Eduardo Habkost 
> ---
>  block.c   |  8 ++--
>  block/raw-posix.c |  8 ++--
>  block/raw_bsd.c   |  4 +---
>  blockdev.c| 16 +---
>  hw/s390x/s390-virtio-ccw.c|  5 +
>  hw/s390x/virtio-ccw.c | 28 +++-
>  scripts/coccinelle/remove_local_err.cocci | 27 +++
>  target-i386/cpu.c |  4 +---
>  8 files changed, 46 insertions(+), 54 deletions(-)
>  create mode 100644 scripts/coccinelle/remove_local_err.cocci
> 

> +++ b/block.c
> @@ -294,14 +294,12 @@ typedef struct CreateCo {
>  
>  static void coroutine_fn bdrv_create_co_entry(void *opaque)
>  {
> -Error *local_err = NULL;
>  int ret;
>  
>  CreateCo *cco = opaque;
>  assert(cco->drv);
>  
> -ret = cco->drv->bdrv_create(cco->filename, cco->opts, _err);
> -error_propagate(>err, local_err);
> +ret = cco->drv->bdrv_create(cco->filename, cco->opts, >err);
>  cco->ret = ret;

This hunk doesn't get simplified by 3/3; you may want to consider a
manual followup to drop 'int ret' and just assign
cco->drv->bdrv_create() directly to cco->ret.  But doesn't change this
patch.


> +++ b/blockdev.c
> @@ -3654,7 +3654,6 @@ void qmp_blockdev_mirror(const char *device, const char 
> *target,
>  BlockBackend *blk;
>  BlockDriverState *target_bs;
>  AioContext *aio_context;
> -Error *local_err = NULL;
>  
>  blk = blk_by_name(device);
>  if (!blk) {
> @@ -3678,16 +3677,11 @@ void qmp_blockdev_mirror(const char *device, const 
> char *target,
>  
>  bdrv_set_aio_context(target_bs, aio_context);
>  
> -blockdev_mirror_common(bs, target_bs,
> -   has_replaces, replaces, sync,
> -   has_speed, speed,
> -   has_granularity, granularity,
> -   has_buf_size, buf_size,
> -   has_on_source_error, on_source_error,
> -   has_on_target_error, on_target_error,
> -   true, true,
> -   _err);
> -error_propagate(errp, local_err);
> +blockdev_mirror_common(bs, target_bs, has_replaces, replaces, sync,
> +   has_speed, speed, has_granularity, granularity,
> +   has_buf_size, buf_size, has_on_source_error,
> +   on_source_error, has_on_target_error,
> +   on_target_error, true, true, errp);

Coccinelle messes a bit with the formatting (the old way explicitly
tried to pair related has_foo with foo). But I'm going to mess with it
again with my qapi patches for passing a boxed parameter rather than
lots of arguments, so don't worry about it.

> +++ b/scripts/coccinelle/remove_local_err.cocci
> @@ -0,0 +1,27 @@
> +// Replace unnecessary usage of local_err variable with
> +// direct usage of errp argument
> +
> +@@
> +expression list ARGS;
> +expression F2;
> +identifier LOCAL_ERR;
> +expression ERRP;
> +idexpression V;
> +typedef Error;
> +expression I;
> +@@
> + {
> + ...
> +-Error *LOCAL_ERR;
> + ... when != LOCAL_ERR
> +(
> +-F2(ARGS, _ERR);
> +-error_propagate(ERRP, LOCAL_ERR);
> ++F2(ARGS, ERRP);
> +|
> +-V = F2(ARGS, _ERR);
> +-error_propagate(ERRP, LOCAL_ERR);
> ++V = F2(ARGS, ERRP);
> +)
> + ... when != LOCAL_ERR
> + }

Looks good.
Reviewed-by: Eric Blake 

-- 
Eric Blake   eblake redhat com+1-919-301-3266
Libvirt virtualization library http://libvirt.org



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[Qemu-devel] [PATCH v2 2/3] error: Remove unnecessary local_err variables

[Eduardo Habkost]

This patch simplifies code that uses a local_err variable just to
immediately use it for an error_propagate() call.

Coccinelle patch used to perform the changes added to
scripts/coccinelle/remove_local_err.cocci.

Signed-off-by: Eduardo Habkost 
---
 block.c   |  8 ++--
 block/raw-posix.c |  8 ++--
 block/raw_bsd.c   |  4 +---
 blockdev.c| 16 +---
 hw/s390x/s390-virtio-ccw.c|  5 +
 hw/s390x/virtio-ccw.c | 28 +++-
 scripts/coccinelle/remove_local_err.cocci | 27 +++
 target-i386/cpu.c |  4 +---
 8 files changed, 46 insertions(+), 54 deletions(-)
 create mode 100644 scripts/coccinelle/remove_local_err.cocci

diff --git a/block.c b/block.c
index ecca55a..d516ab6 100644
--- a/block.c
+++ b/block.c
@@ -294,14 +294,12 @@ typedef struct CreateCo {
 
 static void coroutine_fn bdrv_create_co_entry(void *opaque)
 {
-Error *local_err = NULL;
 int ret;
 
 CreateCo *cco = opaque;
 assert(cco->drv);
 
-ret = cco->drv->bdrv_create(cco->filename, cco->opts, _err);
-error_propagate(>err, local_err);
+ret = cco->drv->bdrv_create(cco->filename, cco->opts, >err);
 cco->ret = ret;
 }
 
@@ -353,7 +351,6 @@ out:
 int bdrv_create_file(const char *filename, QemuOpts *opts, Error **errp)
 {
 BlockDriver *drv;
-Error *local_err = NULL;
 int ret;
 
 drv = bdrv_find_protocol(filename, true, errp);
@@ -361,8 +358,7 @@ int bdrv_create_file(const char *filename, QemuOpts *opts, 
Error **errp)
 return -ENOENT;
 }
 
-ret = bdrv_create(drv, filename, opts, _err);
-error_propagate(errp, local_err);
+ret = bdrv_create(drv, filename, opts, errp);
 return ret;
 }
 
diff --git a/block/raw-posix.c b/block/raw-posix.c
index cb663d8..d7397bf 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -582,12 +582,10 @@ static int raw_open(BlockDriverState *bs, QDict *options, 
int flags,
 Error **errp)
 {
 BDRVRawState *s = bs->opaque;
-Error *local_err = NULL;
 int ret;
 
 s->type = FTYPE_FILE;
-ret = raw_open_common(bs, options, flags, 0, _err);
-error_propagate(errp, local_err);
+ret = raw_open_common(bs, options, flags, 0, errp);
 return ret;
 }
 
@@ -2442,14 +2440,12 @@ static int cdrom_open(BlockDriverState *bs, QDict 
*options, int flags,
   Error **errp)
 {
 BDRVRawState *s = bs->opaque;
-Error *local_err = NULL;
 int ret;
 
 s->type = FTYPE_CD;
 
 /* open will not fail even if no CD is inserted, so add O_NONBLOCK */
-ret = raw_open_common(bs, options, flags, O_NONBLOCK, _err);
-error_propagate(errp, local_err);
+ret = raw_open_common(bs, options, flags, O_NONBLOCK, errp);
 return ret;
 }
 
diff --git a/block/raw_bsd.c b/block/raw_bsd.c
index 5af11b6..b51ac98 100644
--- a/block/raw_bsd.c
+++ b/block/raw_bsd.c
@@ -190,11 +190,9 @@ static int raw_has_zero_init(BlockDriverState *bs)
 
 static int raw_create(const char *filename, QemuOpts *opts, Error **errp)
 {
-Error *local_err = NULL;
 int ret;
 
-ret = bdrv_create_file(filename, opts, _err);
-error_propagate(errp, local_err);
+ret = bdrv_create_file(filename, opts, errp);
 return ret;
 }
 
diff --git a/blockdev.c b/blockdev.c
index 028dba3..3b6d242 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3654,7 +3654,6 @@ void qmp_blockdev_mirror(const char *device, const char 
*target,
 BlockBackend *blk;
 BlockDriverState *target_bs;
 AioContext *aio_context;
-Error *local_err = NULL;
 
 blk = blk_by_name(device);
 if (!blk) {
@@ -3678,16 +3677,11 @@ void qmp_blockdev_mirror(const char *device, const char 
*target,
 
 bdrv_set_aio_context(target_bs, aio_context);
 
-blockdev_mirror_common(bs, target_bs,
-   has_replaces, replaces, sync,
-   has_speed, speed,
-   has_granularity, granularity,
-   has_buf_size, buf_size,
-   has_on_source_error, on_source_error,
-   has_on_target_error, on_target_error,
-   true, true,
-   _err);
-error_propagate(errp, local_err);
+blockdev_mirror_common(bs, target_bs, has_replaces, replaces, sync,
+   has_speed, speed, has_granularity, granularity,
+   has_buf_size, buf_size, has_on_source_error,
+   on_source_error, has_on_target_error,
+   on_target_error, true, true, errp);
 
 aio_context_release(aio_context);
 }
diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index 95ff5e3..b7112d0 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c