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From: Dan Williams <dan.j.williams@intel.com>
To: Jingqi Liu <jingqi.liu@intel.com>
Cc: nvdimm@lists.linux.dev
Subject: Re: [PATCH] ndctl/dimm: Fix to dump namespace indexs and labels
Date: Mon, 7 Jun 2021 13:03:15 -0700	[thread overview]
Message-ID: <CAPcyv4hzS93k5PYXE_bVp6SQ8WwPw09B+SyJC0xPKE20simwuQ@mail.gmail.com> (raw)
In-Reply-To: <20210603012556.77451-1-jingqi.liu@intel.com>

On Wed, Jun 2, 2021 at 6:36 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.
>
> When reading namespace index and labels, we should read the field of 'mysize'
> in the Label Index Block. Then we can correctly calculate the starting offset
> of another Label Index Block and the following namespace labels.

Good find! I agree this is broken, but I'm not sure this is the way to
fix it. The ndctl enabling is meant to support dumping index blocks
that might be corrupt, so I don't want to rely on index block data for
this value. It should copy the kernel which has this definition for
determining sizeof_namespace_index():

size_t sizeof_namespace_index(struct nvdimm_drvdata *ndd)
{
        u32 nslot, space, size;

        /*
         * Per UEFI 2.7, the minimum size of the Label Storage Area is large
         * enough to hold 2 index blocks and 2 labels.  The minimum index
         * block size is 256 bytes. The label size is 128 for namespaces
         * prior to version 1.2 and at minimum 256 for version 1.2 and later.
         */
        nslot = nvdimm_num_label_slots(ndd);
        space = ndd->nsarea.config_size - nslot * sizeof_namespace_label(ndd);
        size = __sizeof_namespace_index(nslot) * 2;
        if (size <= space && nslot >= 2)
                return size / 2;

        dev_err(ndd->dev, "label area (%d) too small to host (%d byte)
labels\n",
                        ndd->nsarea.config_size, sizeof_namespace_label(ndd));
        return 0;
}

  reply	other threads:[~2021-06-07 20:03 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-03  1:25 Jingqi Liu
2021-06-07 20:03 ` Dan Williams [this message]
2021-06-09  1:27   ` Liu, Jingqi
  -- strict thread matches above, loose matches on Subject: below --
2021-06-09  3:06 Jingqi Liu
2021-06-16  1:31 ` Liu, Jingqi
2021-07-02  4:41 ` Dan Williams
2021-07-08  0:21 ` Verma, Vishal L
2021-07-08  1:53   ` Liu, Jingqi
2021-07-08  5:59     ` Verma, Vishal L
2021-07-08  6:52       ` Liu, Jingqi
2021-06-02 12:18 Jingqi Liu

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