On Wed, Nov 29, 2017 at 08:33:29AM +0800, Haozhong Zhang wrote: > On 11/27/17 23:07 -0200, Eduardo Habkost wrote: > > On Mon, Nov 27, 2017 at 12:35:15PM +0800, Haozhong Zhang wrote: > > > When mmap(2) the backend files, QEMU uses the host page size > > > (getpagesize(2)) by default as the alignment of mapping address. > > > However, some backends may require alignments different than the page > > > size. For example, mmap a device DAX (e.g., /dev/dax0.0) on Linux > > > kernel 4.13 to an address, which is 4K-aligned but not 2M-aligned, > > > fails with a kernel message like > > > > > > [617494.969768] dax dax0.0: qemu-system-x86: dax_mmap: fail, unaligned > > > vma (0x7fa37c579000 - 0x7fa43c579000, 0x1fffff) > > > > > > Because there is no common approach to get such alignment requirement, > > > we add the 'align' option to 'memory-backend-file', so that users or > > > management utils, which have enough knowledge about the backend, can > > > specify a proper alignment via this option. > > > > > > Signed-off-by: Haozhong Zhang <haozhong.zh...@intel.com> > > > > The new option needs to be documented on qemu-options.hx. > > will add in the next version.
Note that there are patches on on machine-next that change the memory backend documentation. See: git://github.com/ehabkost/qemu.git machine-next https://github.com/ehabkost/qemu/commit/869f7f61c557a46b46e41b5e38a61551d45b6d0d But the conflicts should be trivial to solve if you document the new option in a separate paragraph. -- Eduardo
