On 05/30/17 10:16 +0100, Stefan Hajnoczi wrote: > On Fri, May 26, 2017 at 10:24:38AM +0800, Haozhong Zhang wrote: > > file_ram_alloc() currently maps the backend file via mmap to a virtual > > address aligned to the value returned by qemu_fd_getpagesize(). When a > > DAX device (e.g. /dev/dax0.0) is used as the backend file, its kernel > > mmap implementation may require an alignment larger than what > > qemu_fd_get_pagesize() returns (e.g. 2MB vs. 4KB), and mmap may fail. > > > > This commit adds an attribute 'align' to hostmem-file, so that users > > can specify a proper alignment that satisfies the kernel requirement. > > > > If 'align' is not specified or is 0, the value returned by > > qemu_fd_get_pagesize() will be used as before. > > How are users supposed to determine alignment requirements?
As discussed in another thread [1,2], the alignment of device-dax can be got from /sys/dev/char/$major:$minor/device/align, and I'll let QEMU read the value from it instead of user input. [1] https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg06235.html [2] https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg06189.html Haozhong
