On Wed, Jun 2, 2021 at 6:36 PM Jingqi Liu <[email protected]> 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;
}
