[Qemu-devel] [PATCH v3 0/3] nvdimm: support MAP_SYNC for memory-backend-file

[Haozhong Zhang]

v3 is based on Eduardo's machine-next tree. Changes of
memory-backend-file are based on my previous patches in that tree.


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 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 (3):
  util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap()
  hostmem: add hostmem type name and id in error messages
  hostmem-file: add 'sync' option

 backends/hostmem-file.c   | 49 +++++++++++++++++++++++++++++++++++++++++++----
 backends/hostmem.c        | 11 +++++++----
 docs/nvdimm.txt           | 15 ++++++++++++++-
 exec.c                    | 13 ++++++++-----
 include/exec/memory.h     |  4 ++++
 include/exec/ram_addr.h   |  6 +++---
 include/qemu/mmap-alloc.h |  3 ++-
 include/qemu/osdep.h      | 18 +++++++++++++++++
 memory.c                  |  6 ++++--
 numa.c                    |  2 +-
 qemu-options.hx           | 21 +++++++++++++++++++-
 util/mmap-alloc.c         | 24 +++++++++++++++++++++--
 util/oslib-posix.c        |  2 +-
 13 files changed, 149 insertions(+), 25 deletions(-)

-- 
2.14.1