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From: Peter Maydell <peter.maydell@linaro.org>
To: Max Reitz <mreitz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>,
	Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
	QEMU Developers <qemu-devel@nongnu.org>,
	Qemu-block <qemu-block@nongnu.org>
Subject: Re: [PULL 33/36] block/backup: use backup-top instead of write notifiers
Date: Thu, 17 Oct 2019 13:04:42 +0100
Message-ID: <CAFEAcA_jV_C1W_EsffV2vv9FjupV2ONTZ1wOxTLBmy76Gh5FgQ@mail.gmail.com> (raw)
In-Reply-To: <20191010114300.7746-34-mreitz@redhat.com>

On Thu, 10 Oct 2019 at 12:44, Max Reitz <mreitz@redhat.com> wrote:
>
> From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>
> Drop write notifiers and use filter node instead.

Hi; after this change Coverity complains about dead code in
backup_job_create() (CID 1406402):

> @@ -382,6 +353,8 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
>      BackupBlockJob *job = NULL;
>      int64_t cluster_size;
>      BdrvRequestFlags write_flags;
> +    BlockDriverState *backup_top = NULL;
> +    BlockCopyState *bcs = NULL;
>
>      assert(bs);
>      assert(target);
> @@ -463,33 +436,35 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
>      write_flags = (bdrv_chain_contains(target, bs) ? BDRV_REQ_SERIALISING : 0) |
>                    (compress ? BDRV_REQ_WRITE_COMPRESSED : 0),
>
> +    backup_top = bdrv_backup_top_append(bs, target, filter_node_name,
> +                                        cluster_size, write_flags, &bcs, errp);
> +    if (!backup_top) {
> +        goto error;
> +    }
> +
>      /* job->len is fixed, so we can't allow resize */
> -    job = block_job_create(job_id, &backup_job_driver, txn, bs, 0, BLK_PERM_ALL,
> +    job = block_job_create(job_id, &backup_job_driver, txn, backup_top,
> +                           0, BLK_PERM_ALL,
>                             speed, creation_flags, cb, opaque, errp);
>      if (!job) {
>          goto error;
>      }
>
> +    job->backup_top = backup_top;
>      job->source_bs = bs;
>      job->on_source_error = on_source_error;
>      job->on_target_error = on_target_error;
>      job->sync_mode = sync_mode;
>      job->sync_bitmap = sync_bitmap;
>      job->bitmap_mode = bitmap_mode;
> -
> -    job->bcs = block_copy_state_new(bs, target, cluster_size, write_flags,
> -                                    errp);
> -    if (!job->bcs) {
> -        goto error;
> -    }
> -

This code deletion has removed the only code path that can
reach the 'error' label after the successful creation of the job...

> +    job->bcs = bcs;
>      job->cluster_size = cluster_size;
>      job->len = len;
>
> -    block_copy_set_callbacks(job->bcs, backup_progress_bytes_callback,
> +    block_copy_set_callbacks(bcs, backup_progress_bytes_callback,
>                               backup_progress_reset_callback, job);
>
> -    /* Required permissions are already taken by block-copy-state target */
> +    /* Required permissions are already taken by backup-top target */
>      block_job_add_bdrv(&job->common, "target", target, 0, BLK_PERM_ALL,
>                         &error_abort);
>
> @@ -502,6 +477,8 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
>      if (job) {
>          backup_clean(&job->common.job);
>          job_early_fail(&job->common.job);

...so down here in the 'error:' code the "if (job)" condition
can never pass, and the code in this part of the if statement
is dead.

> +    } else if (backup_top) {
> +        bdrv_backup_top_drop(backup_top);
>      }
>
>      return NULL;
>  {"return": {}}

thanks
-- PMM


  reply index

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-10 11:42 [PULL 00/36] Block patches Max Reitz
2019-10-10 11:42 ` [PULL 01/36] qemu-iotests: ignore leaks on failure paths in 026 Max Reitz
2019-10-10 11:42 ` [PULL 02/36] block: introduce aio task pool Max Reitz
2019-10-10 11:42 ` [PULL 03/36] block/qcow2: refactor qcow2_co_preadv_part Max Reitz
2019-10-10 11:42 ` [PULL 04/36] block/qcow2: refactor qcow2_co_pwritev_part Max Reitz
2019-10-10 11:42 ` [PULL 05/36] block/qcow2: introduce parallel subrequest handling in read and write Max Reitz
2019-10-10 11:42 ` [PULL 06/36] block/backup: fix max_transfer handling for copy_range Max Reitz
2019-10-10 11:42 ` [PULL 07/36] block/backup: fix backup_cow_with_offload for last cluster Max Reitz
2019-10-10 11:42 ` [PULL 08/36] block/backup: split shareable copying part from backup_do_cow Max Reitz
2019-10-10 11:42 ` [PULL 09/36] block/backup: improve comment about image fleecing Max Reitz
2019-10-10 11:42 ` [PULL 10/36] block/backup: introduce BlockCopyState Max Reitz
2019-10-10 11:42 ` [PULL 11/36] block/backup: fix block-comment style Max Reitz
2019-10-10 11:42 ` [PULL 12/36] block: move block_copy from block/backup.c to separate file Max Reitz
2019-10-10 11:42 ` [PULL 13/36] block: teach bdrv_debug_breakpoint skip filters with backing Max Reitz
2019-10-10 11:42 ` [PULL 14/36] iotests: prepare 124 and 257 bitmap querying for backup-top filter Max Reitz
2019-10-10 11:42 ` [PULL 15/36] iotests: 257: drop unused Drive.device field Max Reitz
2019-10-10 11:42 ` [PULL 16/36] iotests: 257: drop device_add Max Reitz
2019-10-10 11:42 ` [PULL 17/36] qapi: group BlockDeviceStats fields Max Reitz
2019-10-10 11:42 ` [PULL 18/36] qapi: add unmap to BlockDeviceStats Max Reitz
2019-10-10 11:42 ` [PULL 19/36] block: add empty account cookie type Max Reitz
2019-10-10 11:42 ` [PULL 20/36] ide: account UNMAP (TRIM) operations Max Reitz
2019-10-10 11:42 ` [PULL 21/36] scsi: store unmap offset and nb_sectors in request struct Max Reitz
2019-10-10 11:42 ` [PULL 22/36] scsi: move unmap error checking to the complete callback Max Reitz
2019-10-10 11:42 ` [PULL 23/36] scsi: account unmap operations Max Reitz
2019-10-10 11:42 ` [PULL 24/36] file-posix: account discard operations Max Reitz
2019-10-10 11:42 ` [PULL 25/36] qapi: query-blockstat: add driver specific file-posix stats Max Reitz
2019-10-10 11:42 ` [PULL 26/36] iotests: Fix 125 for growth_mode = metadata Max Reitz
2019-10-10 11:42 ` [PULL 27/36] iotests: Disable 125 on broken XFS versions Max Reitz
2019-10-10 11:42 ` [PULL 28/36] iotests: Use stat -c %b in 125 Max Reitz
2019-10-10 11:42 ` [PULL 29/36] block/backup: move in-flight requests handling from backup to block-copy Max Reitz
2019-10-10 11:42 ` [PULL 30/36] block/backup: move write_flags calculation inside backup_job_create Max Reitz
2019-10-10 11:42 ` [PULL 31/36] block/block-copy: split block_copy_set_callbacks function Max Reitz
2019-10-10 11:42 ` [PULL 32/36] block: introduce backup-top filter driver Max Reitz
2019-10-10 11:42 ` [PULL 33/36] block/backup: use backup-top instead of write notifiers Max Reitz
2019-10-17 12:04   ` Peter Maydell [this message]
2019-10-17 13:40     ` Vladimir Sementsov-Ogievskiy
2019-10-10 11:42 ` [PULL 34/36] nbd: add empty .bdrv_reopen_prepare Max Reitz
2019-10-10 11:42 ` [PULL 35/36] tests: fix I/O test for hosts defaulting to LUKSv2 Max Reitz
2019-10-10 11:43 ` [PULL 36/36] iotests/162: Fix for newer Linux 5.3+ Max Reitz
2019-10-14 12:34 ` [PULL 00/36] Block patches Peter Maydell

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