zero_info_block: skip seed devices

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Brew: 

commit fb13dfb8d84c4f0a749665c8f07179450b199f3e

Author: Jeff Moyer <jmoyer@redhat.com>

Date:   Tue Feb 9 16:51:53 2021 -0500

    zero_info_block: skip seed devices

    Currently, ndctl destroy-namespace -f all will output errors of the

    form:

      Error: destroy namespace: namespace0.0 failed to enable for zeroing, continuing

    for any zero-sized namespace.  That particular namespace looks like this:

      {

        "dev":"namespace0.0",

        "mode":"raw",

        "size":0,

        "uuid":"00000000-0000-0000-0000-000000000000",

        "sector_size":512,

        "state":"disabled"

      }

    This patch skips over namespaces with size=0 when zeroing out info

    blocks.

    Fixes: 46654c2d60b70 ("ndctl/namespace: Always zero info-blocks")

    Reported-by: Zhang Yi <yizhan@redhat.com>

    Signed-off-by: Jeff Moyer <jmoyer@redhat.com>

    Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>

    Link: https://lore.kernel.org/r/x49r1lohpty.fsf@segfault.boston.devel.redhat.com

diff --git a/ndctl/namespace.c b/ndctl/namespace.c

index 1feb74d..1e8a2cd 100644

--- a/ndctl/namespace.c

+++ b/ndctl/namespace.c

@@ -1052,6 +1052,9 @@ static int zero_info_block(struct ndctl_namespace *ndns)

 	void *buf = NULL, *read_buf = NULL;

 	char path[50];

+	if (ndctl_namespace_get_size(ndns) == 0)

+		return 1;

+

 	ndctl_namespace_set_raw_mode(ndns, 1);

 	rc = ndctl_namespace_enable(ndns);

 	if (rc < 0) {