Re: [PATCH] ndctl/dimm: Fix to dump namespace indexs and labels

From: Dan Williams <dan.j.williams@intel.com>
To: Jingqi Liu <jingqi.liu@intel.com>
Cc: Linux NVDIMM <nvdimm@lists.linux.dev>,
	Vishal L Verma <vishal.l.verma@intel.com>
Subject: Re: [PATCH] ndctl/dimm: Fix to dump namespace indexs and labels
Date: Thu, 1 Jul 2021 21:41:44 -0700	[thread overview]
Message-ID: <CAPcyv4jZ4WznktzoEm=vousG2rBaV6nyZDj-i8o5TYG=xdTqjg@mail.gmail.com> (raw)
In-Reply-To: <20210609030642.66204-1-jingqi.liu@intel.com>

[ add Vishal ]

On Tue, Jun 8, 2021 at 8:16 PM Jingqi Liu <jingqi.liu@intel.com> wrote:
>
> The following bug is caused by setting the size of Label Index Block
> to a fixed 256 bytes.
>
> Use the following Qemu command to start a Guest with 2MB label-size:
>         -object memory-backend-file,id=mem1,share=on,mem-path=/dev/dax1.1,size=14G,align=2M
>         -device nvdimm,memdev=mem1,id=nv1,label-size=2M
>
> There is a namespace in the Guest as follows:
>         $ ndctl list
>         [
>           {
>             "dev":"namespace0.0",
>             "mode":"devdax",
>             "map":"dev",
>             "size":14780727296,
>             "uuid":"58ad5282-5a16-404f-b8ee-e28b4c784eb8",
>             "chardev":"dax0.0",
>             "align":2097152,
>             "name":"namespace0.0"
>           }
>         ]
>
> Fail to read labels. The result is as follows:
>         $ ndctl read-labels -u nmem0
>         [
>         ]
>         read 0 nmem
>
> If using the following Qemu command to start the Guest with 128K
> label-size, this label can be read correctly.
>         -object memory-backend-file,id=mem1,share=on,mem-path=/dev/dax1.1,size=14G,align=2M
>         -device nvdimm,memdev=mem1,id=nv1,label-size=128K
>
> The size of a Label Index Block depends on how many label slots fit into
> the label storage area. The minimum size of an index block is 256 bytes
> and the size must be a multiple of 256 bytes. For a storage area of 128KB,
> the corresponding Label Index Block size is 256 bytes. But if the label
> storage area is not 128KB, the Label Index Block size should not be 256 bytes.
>
> Namespace Label Index Block appears twice at the top of the label storage area.
> Following the two index blocks, an array for storing labels takes up the
> remainder of the label storage area.
>
> For obtaining the size of Namespace Index Block, we also cannot rely on
> the field of 'mysize' in this index block since it might be corrupted.
> Similar to the linux kernel, we use sizeof_namespace_index() to get the size
> of Namespace Index Block. Then we can also correctly calculate the starting
> offset of the following namespace labels.
>
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>

Apologies for the delay in responding, this looks good and passes my tests:

Reviewed-by: Dan Williams <dan.j.williams@intel.com>