Linux 4.15 introduces a new mmap flag MAP_SYNC, which can be used to guarantee the write persistence to mmap'ed files supporting DAX (e.g., files on ext4/xfs file system mounted with '-o dax').
A description of MAP_SYNC and MAP_SHARED_VALIDATE can be found at https://patchwork.kernel.org/patch/10028151/ This patchset enables QEMU to use MAP_SYNC flag for memory-backend-file, in order to guarantee the guest write persistence to backend files supporting DAX. A new auto on/off option 'sync' is added to memory-backend-file: - on: try to pass MAP_SYNC to mmap(2); if MAP_SYNC is not supported or 'share=off', QEMU will abort - off: never pass MAP_SYNC to mmap(2) - auto (default): if MAP_SYNC is supported and 'share=on', work as if 'sync=on'; otherwise, work as if 'sync=off' Changes in v4: * Add patch 1-3 to switch some functions to a single 'flags' parameters. (Michael S. Tsirkin) * v3 patch 1-3 become v4 patch 4-6. * Patch 4: move definitions of MAP_SYNC and MAP_SHARED_VALIDATE to a new header file under include/standard-headers/linux/. (Michael S. Tsirkin) * Patch 6: refine the description of the 'sync' option. (Michael S. Tsirkin) Changes in v3: * Patch 1: add MAP_SHARED_VALIDATE in both sync=on and sync=auto cases, and add back the retry mechanism. MAP_SYNC will be ignored by Linux kernel 4.15 if MAP_SHARED_VALIDATE is missed. * Patch 1: define MAP_SYNC and MAP_SHARED_VALIDATE as 0 on non-Linux platforms in order to make qemu_ram_mmap() compile on those platforms. * Patch 2&3: include more information in error messages of memory-backend in hope to help user to identify the error. (Dr. David Alan Gilbert) * Patch 3: fix typo in the commit message. (Dr. David Alan Gilbert) Changes in v2: * Add 'sync' option to control the use of MAP_SYNC. (Eduardo Habkost) * Remove the unnecessary set of MAP_SHARED_VALIDATE in some cases and the retry mechanism in qemu_ram_mmap(). (Michael S. Tsirkin) * Move OS dependent definitions of MAP_SYNC and MAP_SHARED_VALIDATE to osdep.h. (Michael S. Tsirkin) Haozhong Zhang (6): util/mmap-alloc: switch qemu_ram_mmap() to 'flags' parameter exec: switch qemu_ram_alloc_from_{file,fd} to the 'flags' parameter memory: switch memory_region_init_ram_from_file() to 'flags' parameter util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap() hostmem: add more information in error messages hostmem-file: add 'sync' option backends/hostmem-file.c | 51 ++++++++++++++++++++++++++++++++--- backends/hostmem.c | 11 +++++--- docs/nvdimm.txt | 20 +++++++++++++- exec.c | 15 ++++++----- include/exec/memory.h | 36 +++++++++++++++++++++++-- include/exec/ram_addr.h | 29 ++++++++++++++++++-- include/qemu/mmap-alloc.h | 23 +++++++++++++++- include/standard-headers/linux/mman.h | 42 +++++++++++++++++++++++++++++ memory.c | 8 +++--- numa.c | 2 +- qemu-options.hx | 22 ++++++++++++++- util/mmap-alloc.c | 31 ++++++++++++++++++--- util/oslib-posix.c | 2 +- 13 files changed, 261 insertions(+), 31 deletions(-) create mode 100644 include/standard-headers/linux/mman.h -- 2.14.1