[v3,09/15] util/mmap-alloc: Factor out populating of memory to mmap_populate()

Commit Message

David Hildenbrand Feb. 27, 2020, 10:11 a.m. UTC

We want to populate memory within a reserved memory region. Let's factor
that out.

Reviewed-by: Richard Henderson <[e-mail]>
Acked-by: Murilo Opsfelder Araujo <[e-mail]>
Reviewed-by: Peter Xu <[e-mail]>
Cc: Igor Kotrasinski <[e-mail]>
Cc: "Michael S. Tsirkin" <[e-mail]>
Cc: Greg Kurz <[e-mail]>
Cc: Murilo Opsfelder Araujo <[e-mail]>
Cc: Eduardo Habkost <[e-mail]>
Cc: "Dr. David Alan Gilbert" <[e-mail]>
Cc: Igor Mammedov <[e-mail]>
Signed-off-by: David Hildenbrand <[e-mail]>
---
 util/mmap-alloc.c | 89 +++++++++++++++++++++++++----------------------
 1 file changed, 47 insertions(+), 42 deletions(-)

Comments

David Hildenbrand March 3, 2020, 8:43 a.m. UTC | #1

On 27.02.20 11:11, David Hildenbrand wrote:
> We want to populate memory within a reserved memory region. Let's factor
> that out.
> 
> Reviewed-by: Richard Henderson <[e-mail]>
> Acked-by: Murilo Opsfelder Araujo <[e-mail]>
> Reviewed-by: Peter Xu <[e-mail]>
> Cc: Igor Kotrasinski <[e-mail]>
> Cc: "Michael S. Tsirkin" <[e-mail]>
> Cc: Greg Kurz <[e-mail]>
> Cc: Murilo Opsfelder Araujo <[e-mail]>
> Cc: Eduardo Habkost <[e-mail]>
> Cc: "Dr. David Alan Gilbert" <[e-mail]>
> Cc: Igor Mammedov <[e-mail]>
> Signed-off-by: David Hildenbrand <[e-mail]>

Thought a bit longer about the terminology (as brought up by Peter).
Populate might indeed be confusing, because we are not actually
populating all memory (e.g., MAP_POPULATE). We enable/activate the
mapping to be accessible.

Hmmm

mmap_enable() ?

mmap_activate() ?

I think I like the latter. Alternatives?

Patch

diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
index 9e9534a07e..73179f36d6 100644
--- a/util/mmap-alloc.c
+++ b/util/mmap-alloc.c
@@ -114,6 +114,50 @@  static void *mmap_reserve(size_t size, int fd)
     return mmap(0, size, PROT_NONE, flags, fd, 0);
 }
 
+/*
+ * Populate memory in a reserved region from the given fd (if any).
+ */
+static void *mmap_populate(void *ptr, size_t size, int fd, bool shared,
+                           bool is_pmem)
+{
+    int map_sync_flags = 0;
+    int flags = MAP_FIXED;
+    void *populated_ptr;
+
+    flags |= fd == -1 ? MAP_ANONYMOUS : 0;
+    flags |= shared ? MAP_SHARED : MAP_PRIVATE;
+    if (shared && is_pmem) {
+        map_sync_flags = MAP_SYNC | MAP_SHARED_VALIDATE;
+    }
+
+    populated_ptr = mmap(ptr, size, PROT_READ | PROT_WRITE,
+                         flags | map_sync_flags, fd, 0);
+    if (populated_ptr == MAP_FAILED && map_sync_flags) {
+        if (errno == ENOTSUP) {
+            char *proc_link = g_strdup_printf("/proc/self/fd/%d", fd);
+            char *file_name = g_malloc0(PATH_MAX);
+            int len = readlink(proc_link, file_name, PATH_MAX - 1);
+
+            if (len < 0) {
+                len = 0;
+            }
+            file_name[len] = '\0';
+            fprintf(stderr, "Warning: requesting persistence across crashes "
+                    "for backend file %s failed. Proceeding without "
+                    "persistence, data might become corrupted in case of host "
+                    "crash.\n", file_name);
+            g_free(proc_link);
+            g_free(file_name);
+        }
+        /*
+         * If mmap failed with MAP_SHARED_VALIDATE | MAP_SYNC, we will try
+         * again without these flags to handle backwards compatibility.
+         */
+        populated_ptr = mmap(ptr, size, PROT_READ | PROT_WRITE, flags, fd, 0);
+    }
+    return populated_ptr;
+}
+
 static inline size_t mmap_guard_pagesize(int fd)
 {
 #if defined(__powerpc64__) && defined(__linux__)
@@ -131,12 +175,8 @@  void *qemu_ram_mmap(int fd,
                     bool is_pmem)
 {
     const size_t guard_pagesize = mmap_guard_pagesize(fd);
-    int flags;
-    int map_sync_flags = 0;
-    size_t offset;
-    size_t total;
-    void *guardptr;
-    void *ptr;
+    size_t offset, total;
+    void *ptr, *guardptr;
 
     /*
      * Note: this always allocates at least one extra page of virtual address
@@ -153,44 +193,9 @@  void *qemu_ram_mmap(int fd,
     /* Always align to host page size */
     assert(align >= guard_pagesize);
 
-    flags = MAP_FIXED;
-    flags |= fd == -1 ? MAP_ANONYMOUS : 0;
-    flags |= shared ? MAP_SHARED : MAP_PRIVATE;
-    if (shared && is_pmem) {
-        map_sync_flags = MAP_SYNC | MAP_SHARED_VALIDATE;
-    }
-
     offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr;
 
-    ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
-               flags | map_sync_flags, fd, 0);
-
-    if (ptr == MAP_FAILED && map_sync_flags) {
-        if (errno == ENOTSUP) {
-            char *proc_link, *file_name;
-            int len;
-            proc_link = g_strdup_printf("/proc/self/fd/%d", fd);
-            file_name = g_malloc0(PATH_MAX);
-            len = readlink(proc_link, file_name, PATH_MAX - 1);
-            if (len < 0) {
-                len = 0;
-            }
-            file_name[len] = '\0';
-            fprintf(stderr, "Warning: requesting persistence across crashes "
-                    "for backend file %s failed. Proceeding without "
-                    "persistence, data might become corrupted in case of host "
-                    "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 = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
-                   flags, fd, 0);
-    }
-
+    ptr = mmap_populate(guardptr + offset, size, fd, shared, is_pmem);
     if (ptr == MAP_FAILED) {
         munmap(guardptr, total);
         return MAP_FAILED;