Re: [Qemu-devel] [PATCH 12/14] block: Clean up reopen_backing_file() in block/replication.c

[Max Reitz]

On 19.09.18 16:47, Alberto Garcia wrote:
> This function is used to put the hidden and secondary disks in
> read-write mode before launching the backup job, and back in read-only
> mode afterwards.
> 
> This patch does the following changes:
> 
>   - Use an options QDict with the "read-only" option instead of
>     passing the changes as flags only.
> 
>   - Simplify the code (it was unnecessarily complicated and verbose).
> 
>   - Fix a bug due to which the secondary disk was not being put back
>     in read-only mode when writable=false (because in this case
>     orig_secondary_flags always had the BDRV_O_RDWR flag set).
> 
>   - Stop clearing the BDRV_O_INACTIVE flag.

Why?  Sorry, but I don't know much about replication.  Do you know this
change is OK?  (Since the code deliberately clears it right now.)

(Well, it makes sense not to re-set it afterwards...)

> The flags parameter to bdrv_reopen_queue() becomes redundant and we'll
> be able to get rid of it in a subsequent patch.
> 
> Signed-off-by: Alberto Garcia <address@hidden>
> ---
>  block/replication.c | 42 ++++++++++++++++++------------------------
>  1 file changed, 18 insertions(+), 24 deletions(-)
> 
> diff --git a/block/replication.c b/block/replication.c
> index 6349d6958e..1ad0ef2ef8 100644
> --- a/block/replication.c
> +++ b/block/replication.c
> @@ -20,6 +20,7 @@
>  #include "block/block_backup.h"
>  #include "sysemu/block-backend.h"
>  #include "qapi/error.h"
> +#include "qapi/qmp/qdict.h"
>  #include "replication.h"
>  
>  typedef enum {
> @@ -39,8 +40,8 @@ typedef struct BDRVReplicationState {
>      char *top_id;
>      ReplicationState *rs;
>      Error *blocker;
> -    int orig_hidden_flags;
> -    int orig_secondary_flags;
> +    bool orig_hidden_read_only;
> +    bool orig_secondary_read_only;
>      int error;
>  } BDRVReplicationState;
>  
> @@ -376,39 +377,32 @@ static void reopen_backing_file(BlockDriverState *bs, 
> bool writable,
>  {
>      BDRVReplicationState *s = bs->opaque;
>      BlockReopenQueue *reopen_queue = NULL;
> -    int orig_hidden_flags, orig_secondary_flags;
> -    int new_hidden_flags, new_secondary_flags;
>      Error *local_err = NULL;
>  
>      if (writable) {

I'd like to request a comment that "writable" is true the first time
this function is called, and false the second time.  That'd make it
clear why this rewrite makes sense.

(And that writable=false means reverting to the original state.)

((And no, it doesn't make more sense before this patch.))

> -        orig_hidden_flags = s->orig_hidden_flags =
> -                                bdrv_get_flags(s->hidden_disk->bs);
> -        new_hidden_flags = (orig_hidden_flags | BDRV_O_RDWR) &
> -                                                    ~BDRV_O_INACTIVE;
> -        orig_secondary_flags = s->orig_secondary_flags =
> -                                bdrv_get_flags(s->secondary_disk->bs);
> -        new_secondary_flags = (orig_secondary_flags | BDRV_O_RDWR) &
> -                                                     ~BDRV_O_INACTIVE;
> -    } else {
> -        orig_hidden_flags = (s->orig_hidden_flags | BDRV_O_RDWR) &
> -                                                    ~BDRV_O_INACTIVE;
> -        new_hidden_flags = s->orig_hidden_flags;
> -        orig_secondary_flags = (s->orig_secondary_flags | BDRV_O_RDWR) &
> -                                                    ~BDRV_O_INACTIVE;
> -        new_secondary_flags = s->orig_secondary_flags;
> +        s->orig_hidden_read_only =
> +            !(bdrv_get_flags(s->hidden_disk->bs) & BDRV_O_RDWR);
> +        s->orig_secondary_read_only =
> +            !(bdrv_get_flags(s->secondary_disk->bs) & BDRV_O_RDWR);

Why not use bdrv_is_read_only()?

Max

>      }
>  
>      bdrv_subtree_drained_begin(s->hidden_disk->bs);
>      bdrv_subtree_drained_begin(s->secondary_disk->bs);
>  
> -    if (orig_hidden_flags != new_hidden_flags) {
> -        reopen_queue = bdrv_reopen_queue(reopen_queue, s->hidden_disk->bs, 
> NULL,
> -                                         new_hidden_flags);
> +    if (s->orig_hidden_read_only) {
> +        int flags = bdrv_get_flags(s->hidden_disk->bs);
> +        QDict *opts = qdict_new();
> +        qdict_put_bool(opts, BDRV_OPT_READ_ONLY, !writable);
> +        reopen_queue = bdrv_reopen_queue(reopen_queue, s->hidden_disk->bs,
> +                                         opts, flags);
>      }
>  
> -    if (!(orig_secondary_flags & BDRV_O_RDWR)) {
> +    if (s->orig_secondary_read_only) {
> +        int flags = bdrv_get_flags(s->secondary_disk->bs);
> +        QDict *opts = qdict_new();
> +        qdict_put_bool(opts, BDRV_OPT_READ_ONLY, !writable);
>          reopen_queue = bdrv_reopen_queue(reopen_queue, s->secondary_disk->bs,
> -                                         NULL, new_secondary_flags);
> +                                         opts, flags);
>      }
>  
>      if (reopen_queue) {
>

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