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docs/nvdimm: add description of alignment requirement of device dax

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For device dax (e.g., /dev/dax0.0), the NUM of 'align=NUM' option
needs to match the alignment requirement of the device dax.
It must be larger than or equal to the 'align' of device dax.

Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
Message-Id: <20200429085011.63752-3-jingqi.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Jingqi Liu 2020-04-29 16:50:10 +08:00 committed by Paolo Bonzini
parent ce317be98d
commit 5f509751f7
2 changed files with 11 additions and 1 deletions
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10
docs/nvdimm.txt
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@ -132,6 +132,16 @@ address to the page size (getpagesize(2)) by default. However, some
types of backends may require an alignment different than the page
size. In that case, QEMU v2.12.0 and later provide 'align' option to
memory-backend-file to allow users to specify the proper alignment.
For device dax (e.g., /dev/dax0.0), this alignment needs to match the
alignment requirement of the device dax. The NUM of 'align=NUM' option
must be larger than or equal to the 'align' of device dax.
We can use one of the following commands to show the 'align' of device dax.
ndctl list -X
daxctl list -R
In order to get the proper 'align' of device dax, you need to install
the library 'libdaxctl'.
For example, device dax require the 2 MB alignment, so we can use
following QEMU command line options to use it (/dev/dax0.0) as the

2
exec.c
View file

@ -2379,7 +2379,7 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
file_align = get_file_align(fd);
if (file_align > 0 && mr && file_align > mr->align) {
error_setg(errp, "backing store align 0x%" PRIx64
" is larger than 'align' option 0x" PRIx64,
" is larger than 'align' option 0x%" PRIx64,
file_align, mr->align);
return NULL;
}