Implement resizeable mmaps. For now, the actual resizing is not wired up.
Introduce qemu_ram_mmap_resizeable() and qemu_ram_mmap_resize(). Make
qemu_ram_mmap() a wrapper of qemu_ram_mmap_resizeable().
Cc: Richard Henderson
Cc: Igor Kotrasinski
Cc: Murilo Opsfelder Araujo
Cc: "Michael S. Tsirkin"
Cc: Greg Kurz
Cc: Eduardo Habkost
Cc: "Dr. David Alan Gilbert"
Cc: Igor Mammedov
Signed-off-by: David Hildenbrand
---
include/qemu/mmap-alloc.h | 21 +++
util/mmap-alloc.c | 43 ---
2 files changed, 44 insertions(+), 20 deletions(-)
diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
index e786266b92..ca8f7edf70 100644
--- a/include/qemu/mmap-alloc.h
+++ b/include/qemu/mmap-alloc.h
@@ -7,11 +7,13 @@ size_t qemu_fd_getpagesize(int fd);
size_t qemu_mempath_getpagesize(const char *mem_path);
/**
- * qemu_ram_mmap: mmap the specified file or device.
+ * qemu_ram_mmap_resizeable: reserve a memory region of @max_size to mmap the
+ * specified file or device and mmap @size of it.
*
* Parameters:
* @fd: the file or the device to mmap
* @size: the number of bytes to be mmaped
+ * @max_size: the number of bytes to be reserved
* @align: if not zero, specify the alignment of the starting mapping address;
* otherwise, the alignment in use will be determined by QEMU.
* @shared: map has RAM_SHARED flag.
@@ -21,12 +23,15 @@ size_t qemu_mempath_getpagesize(const char *mem_path);
* On success, return a pointer to the mapped area.
* On failure, return MAP_FAILED.
*/
-void *qemu_ram_mmap(int fd,
-size_t size,
-size_t align,
-bool shared,
-bool is_pmem);
-
-void qemu_ram_munmap(int fd, void *ptr, size_t size);
+void *qemu_ram_mmap_resizeable(int fd, size_t size, size_t max_size,
+ size_t align, bool shared, bool is_pmem);
+bool qemu_ram_mmap_resize(void *ptr, int fd, size_t old_size, size_t new_size,
+ bool shared, bool is_pmem);
+static inline void *qemu_ram_mmap(int fd, size_t size, size_t align,
+ bool shared, bool is_pmem)
+{
+return qemu_ram_mmap_resizeable(fd, size, size, align, shared, is_pmem);
+}
+void qemu_ram_munmap(int fd, void *ptr, size_t max_size);
#endif
diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
index c6a6075215..8f9c533f32 100644
--- a/util/mmap-alloc.c
+++ b/util/mmap-alloc.c
@@ -173,11 +173,8 @@ static inline size_t mmap_guard_pagesize(int fd)
#endif
}
-void *qemu_ram_mmap(int fd,
-size_t size,
-size_t align,
-bool shared,
-bool is_pmem)
+void *qemu_ram_mmap_resizeable(int fd, size_t size, size_t max_size,
+ size_t align, bool shared, bool is_pmem)
{
const size_t guard_pagesize = mmap_guard_pagesize(fd);
const size_t pagesize = qemu_fd_getpagesize(fd);
@@ -185,12 +182,14 @@ void *qemu_ram_mmap(int fd,
void *ptr, *guardptr;
g_assert(QEMU_IS_ALIGNED(size, pagesize));
+g_assert(QEMU_IS_ALIGNED(max_size, pagesize));
/*
* Note: this always allocates at least one extra page of virtual address
- * space, even if size is already aligned.
+ * space, even if the size is already aligned. We will reserve an area of
+ * at least max_size, but only populate the requested part of it.
*/
-total = size + align;
+total = max_size + align;
guardptr = mmap_reserve(NULL, total, fd);
if (guardptr == MAP_FAILED) {
@@ -218,21 +217,41 @@ void *qemu_ram_mmap(int fd,
* a guard page guarding against potential buffer overflows.
*/
total -= offset;
-if (total > size + guard_pagesize) {
-munmap(ptr + size + guard_pagesize, total - size - guard_pagesize);
+if (total > max_size + guard_pagesize) {
+munmap(ptr + max_size + guard_pagesize,
+ total - max_size - guard_pagesize);
}
return ptr;
}
-void qemu_ram_munmap(int fd, void *ptr, size_t size)
+bool qemu_ram_mmap_resize(void *ptr, int fd, size_t old_size, size_t new_size,
+ bool shared, bool is_pmem)
{
const size_t pagesize = qemu_fd_getpagesize(fd);
-g_assert(QEMU_IS_ALIGNED(size, pagesize));
+g_assert(QEMU_IS_ALIGNED(old_size, pagesize));
+g_assert(QEMU_IS_ALIGNED(new_size, pagesize));
+
+if (old_size < new_size) {
+/* populate the missing piece into the reserved area */
+ptr = mmap_populate(ptr + old_size, new_size - old_size, fd, old_size,
+shared, is_pmem);
+} else if (old_size > new_size) {
+/* discard this piece, marking it reserved */
+ptr = mmap_reserve(ptr + new_size, old_size - new_size, fd);
+}
+return ptr != MAP_FAILED;
+}
+
+void qemu_ram_munmap(int fd, void *ptr, size_t max_size)
