On 2019-01-23 at 10:04:01 -0500, Michael S. Tsirkin wrote:
> On Wed, Jan 23, 2019 at 10:59:45AM +0800, Zhang, Yi wrote:
> > From: Zhang Yi <yi.z.zh...@linux.intel.com>
> >
> > When a file supporting DAX is used as vNVDIMM backend, mmap it with
> > MAP_SYNC flag in addition which can ensure file system metadata
> > synced in each guest writes to the backend file, without other QEMU
> > actions (e.g., periodic fsync() by QEMU).
> >
> > Current, We have below different possible use cases:
> >
> > 1. pmem=on is set, shared=on is set, MAP_SYNC supported:
> > a: backend is a dax supporting file.
> > - MAP_SYNC will active.
> > b: backend is not a dax supporting file.
> > - mmap will result in an EOPNOTSUPP error.
> >
> > 2. The rest of cases:
> > - we will never pass the MAP_SYNC to mmap2
> >
> > Signed-off-by: Haozhong Zhang <haozhong.zh...@intel.com>
> > Signed-off-by: Zhang Yi <yi.z.zh...@linux.intel.com>
> > ---
> > include/qemu/mmap-alloc.h | 1 +
> > include/qemu/osdep.h | 21 +++++++++++++++++++++
> > util/mmap-alloc.c | 7 ++++++-
> > 3 files changed, 28 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
> > index 6fe6ed4..a95d91c 100644
> > --- a/include/qemu/mmap-alloc.h
> > +++ b/include/qemu/mmap-alloc.h
> > @@ -18,6 +18,7 @@ size_t qemu_mempath_getpagesize(const char *mem_path);
> > * @flags: specifies additional properties of the mapping, which can be
> > one or
> > * bit-or of following values
> > * - RAM_SHARED: mmap with MAP_SHARED flag
> > + * - RAM_PMEM: mmap with MAP_SYNC flag
> > * Other bits are ignored.
> > *
> > * Return:
> > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> > index 457d24e..3bcf155 100644
> > --- a/include/qemu/osdep.h
> > +++ b/include/qemu/osdep.h
> > @@ -419,6 +419,27 @@ void qemu_anon_ram_free(void *ptr, size_t size);
> > # define QEMU_VMALLOC_ALIGN getpagesize()
> > #endif
> >
> > +/*
> > + * MAP_SHARED_VALIDATE and MAP_SYNC are introduced in Linux kernel
> > + * 4.15, so they may not be defined when compiling on older kernels.
> > + */
>
>
> I commented on this part in v7. That's a wrong way to handle
> compatibility.
I'm a little confused that, you point me that should use
#include <linux/mman.h>
here in v9, so what is best way to handle compatibility?
modify the update-linux-headers.sh and copy the mman.h to
standard-headers/linux/?
and #incldue standard-headers/linux/mman.h ?
but it still need fix the compatibility. if the MAP_SYNC not defined in
the old kernel. Right?
forgive me my poor understandings, I'm pazzled.
>
> > +#ifdef CONFIG_LINUX
> > +
> > +#include <linux/mman.h>
> > +
> > +#ifndef MAP_SYNC
> > +#define MAP_SYNC 0x0
> > +#endif
> > +
> > +#ifndef MAP_SHARED_VALIDATE
> > +#define MAP_SHARED_VALIDATE 0x0
> > +#endif
> > +
>
>
>
>
> > +#else /* !CONFIG_LINUX */
> > +#define MAP_SYNC 0x0
> > +#define MAP_SHARED_VALIDATE 0x0
> > +#endif /* CONFIG_LINUX */
> > +
> > #ifdef CONFIG_POSIX
> > struct qemu_signalfd_siginfo {
> > uint32_t ssi_signo; /* Signal number */
> > diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> > index 8f0a740..a4ce9b5 100644
> > --- a/util/mmap-alloc.c
> > +++ b/util/mmap-alloc.c
> > @@ -99,6 +99,8 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align,
> > uint32_t flags)
> > void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1,
> > 0);
> > #endif
> > bool shared = flags & RAM_SHARED;
> > + bool is_pmem = flags & RAM_PMEM;
> > + int mmap_xflags = 0;
> > size_t offset;
> > void *ptr1;
> >
> > @@ -109,12 +111,15 @@ void *qemu_ram_mmap(int fd, size_t size, size_t
> > align, uint32_t flags)
> > assert(is_power_of_2(align));
> > /* Always align to host page size */
> > assert(align >= getpagesize());
> > + if (shared && is_pmem) {
> > + mmap_xflags |= (MAP_SYNC | MAP_SHARED_VALIDATE);
> > + }
> >
> > offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
> > ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
> > MAP_FIXED |
> > (fd == -1 ? MAP_ANONYMOUS : 0) |
> > - (shared ? MAP_SHARED : MAP_PRIVATE),
> > + (shared ? MAP_SHARED : MAP_PRIVATE) | mmap_xflags,
> > fd, 0);
> > if (ptr1 == MAP_FAILED) {
> > munmap(ptr, total);
> > --
> > 2.7.4
