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X-Received-From: 134.134.136.20 Subject: [Qemu-devel] [PATCH v15 1/2] util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap() X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: pagupta@redhat.com, xiaoguangrong.eric@gmail.com, mst@redhat.com, Haozhong Zhang , yi.z.zhang@linux.intel.com, yu.c.zhang@linux.intel.com, richardw.yang@linux.intel.com, stefanha@redhat.com, imammedo@redhat.com, pbonzini@redhat.com, dan.j.williams@intel.com, ehabkost@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Type: text/plain; charset="utf-8" From: Zhang Yi 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=3Don is set, shared=3Don 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 trigger a warning. then MAP_SYNC flag will be ignored 2. The rest of cases: - we will never pass the MAP_SYNC to mmap2 Signed-off-by: Haozhong Zhang Signed-off-by: Zhang Yi [ehabkost: Rebased patch to latest code on master] Signed-off-by: Eduardo Habkost Signed-off-by: Wei Yang Tested-by: Wei Yang Reviewed-by: Stefan Hajnoczi --- v15: fix compile issue on pre-linux4.15 v14: rebase on top of current upstream --- util/mmap-alloc.c | 45 ++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 44 insertions(+), 1 deletion(-) diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c index 9713f4b960..b8f94d618a 100644 --- a/util/mmap-alloc.c +++ b/util/mmap-alloc.c @@ -10,6 +10,17 @@ * later. See the COPYING file in the top-level directory. */ =20 +#ifdef CONFIG_LINUX +#include +#endif /* CONFIG_LINUX */ + +#ifndef MAP_SYNC +#define MAP_SYNC 0 +#endif +#ifndef MAP_SHARED_VALIDATE +#define MAP_SHARED_VALIDATE 0 +#endif + #include "qemu/osdep.h" #include "qemu/mmap-alloc.h" #include "qemu/host-utils.h" @@ -82,6 +93,7 @@ void *qemu_ram_mmap(int fd, bool is_pmem) { int flags; + int map_sync_flags =3D 0; int guardfd; size_t offset; size_t pagesize; @@ -132,9 +144,40 @@ void *qemu_ram_mmap(int fd, flags =3D MAP_FIXED; flags |=3D fd =3D=3D -1 ? MAP_ANONYMOUS : 0; flags |=3D shared ? MAP_SHARED : MAP_PRIVATE; + if (shared && is_pmem) { + map_sync_flags =3D MAP_SYNC | MAP_SHARED_VALIDATE; + } + offset =3D QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guar= dptr; =20 - ptr =3D mmap(guardptr + offset, size, PROT_READ | PROT_WRITE, flags, f= d, 0); + ptr =3D mmap(guardptr + offset, size, PROT_READ | PROT_WRITE, + flags | map_sync_flags, fd, 0); + + if (ptr =3D=3D MAP_FAILED && map_sync_flags) { + if (errno =3D=3D ENOTSUP) { + char *proc_link, *file_name; + int len; + proc_link =3D g_strdup_printf("/proc/self/fd/%d", fd); + file_name =3D g_malloc0(PATH_MAX); + len =3D readlink(proc_link, file_name, PATH_MAX - 1); + if (len < 0) { + len =3D 0; + } + file_name[len] =3D '\0'; + fprintf(stderr, "Warning: requesting persistence across crashe= s " + "for backend file %s failed. Proceeding without " + "persistence, data might become corrupted in case of h= ost " + "crash.\n", file_name); + g_free(proc_link); + g_free(file_name); + } + /* + * if map failed with MAP_SHARED_VALIDATE | MAP_SYNC, + * we will remove these flags to handle compatibility. + */ + ptr =3D mmap(guardptr + offset, size, PROT_READ | PROT_WRITE, + flags, fd, 0); + } =20 if (ptr =3D=3D MAP_FAILED) { munmap(guardptr, total); --=20 2.19.1