[Qemu-devel] [PATCH v5 0/7] nvdimm: support MAP_SYNC for memory-backend-file

[Zhang Yi]

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/

In order to make sure that the file metadata is in sync after a fault 
while we are writing a shared DAX supporting backend files, this
patch-set enables QEMU to use MAP_SYNC flag for memory-backend-dax-file.

As the DAX vs DMA truncated issue was solved, we refined the code and
send out this feature for the v5 version.

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 v5:
 * Add patch 1 to fix a memory leak issue.
 * Refine the patch 4-6
 * Remove the patch 3 as we already change the parameter from "shared" to
   "flags"

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)

Zhang Yi (7):
  numa: Fixed the memory leak of numa error message
  util/mmap-alloc: switch qemu_ram_mmap() to 'flags' parameter
  exec: switch qemu_ram_alloc_from_{file, fd} to the 'flags' parameter
  util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap()
  util/mmap-alloc: Switch the RAM_SYNC flags to OnOffAuto
  hostmem: add more information in error messages
  hostmem-file: add 'sync' option

 backends/hostmem-file.c               | 45 +++++++++++++++++++++++++++++++++--
 backends/hostmem.c                    |  8 ++++---
 docs/nvdimm.txt                       | 20 +++++++++++++++-
 exec.c                                |  9 +++----
 include/exec/memory.h                 | 18 ++++++++++++++
 include/exec/ram_addr.h               |  1 +
 include/qemu/mmap-alloc.h             | 20 +++++++++++++++-
 include/standard-headers/linux/mman.h | 44 ++++++++++++++++++++++++++++++++++
 numa.c                                |  1 +
 qemu-options.hx                       | 22 ++++++++++++++++-
 util/mmap-alloc.c                     | 26 ++++++++++++++++----
 util/oslib-posix.c                    |  4 +++-
 12 files changed, 200 insertions(+), 18 deletions(-)
 create mode 100644 include/standard-headers/linux/mman.h

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2.7.4