Implement resizable mmaps. For now, the actual resizing is not wired up.
Introduce qemu_ram_mmap_resizable() and qemu_ram_mmap_resize(). Make
qemu_ram_mmap() a wrapper of qemu_ram_mmap_resizable().
Cc: "Michael S. Tsirkin" <m...@redhat.com>
Cc: Greg Kurz <gr...@kaod.org>
Cc: Murilo Opsfelder Araujo <muri...@linux.ibm.com>
Cc: Eduardo Habkost <ehabk...@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
Signed-off-by: David Hildenbrand <da...@redhat.com>
---
include/qemu/mmap-alloc.h | 21 ++++++++++++-------
util/mmap-alloc.c | 44 ++++++++++++++++++++++++++++-----------
2 files changed, 45 insertions(+), 20 deletions(-)
diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
index e786266b92..70bc8e9637 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_resizable: 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_resizable(int fd, size_t size, size_t max_size,
+ size_t align, bool shared, bool is_pmem);
+void *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_resizable(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 63ad6893b7..2d562145e9 100644
--- a/util/mmap-alloc.c
+++ b/util/mmap-alloc.c
@@ -172,11 +172,8 @@ static inline size_t mmap_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_resizable(int fd, size_t size, size_t max_size,
+ size_t align, bool shared, bool is_pmem)
{
const size_t pagesize = mmap_pagesize(fd);
size_t offset, total;
@@ -184,12 +181,14 @@ void *qemu_ram_mmap(int fd,
/* we can only map whole pages */
size = QEMU_ALIGN_UP(size, pagesize);
+ max_size = QEMU_ALIGN_UP(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(0, total, fd);
if (guardptr == MAP_FAILED) {
@@ -217,22 +216,43 @@ void *qemu_ram_mmap(int fd,
* a guard page guarding against potential buffer overflows.
*/
total -= offset;
- if (total > size + pagesize) {
- munmap(ptr + size + pagesize, total - size - pagesize);
+ if (total > max_size + pagesize) {
+ munmap(ptr + max_size + pagesize, total - max_size - pagesize);
}
return ptr;
}
-void qemu_ram_munmap(int fd, void *ptr, size_t size)
+void *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 = mmap_pagesize(fd);
/* we can only map whole pages */
- size = QEMU_ALIGN_UP(size, pagesize);
+ old_size = QEMU_ALIGN_UP(old_size, pagesize);
+ new_size = QEMU_ALIGN_UP(new_size, pagesize);
+
+ /* we support actually resizable memory regions only on Linux */
+ 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, keeping the area reserved (should never fail) */
+ ptr = mmap_reserve(ptr + new_size, old_size - new_size, fd);
+ }
+ return ptr;
+}
+
+void qemu_ram_munmap(int fd, void *ptr, size_t max_size)
+{
+ const size_t pagesize = mmap_pagesize(fd);
+
+ /* we can only map whole pages */
+ max_size = QEMU_ALIGN_UP(max_size, pagesize);
if (ptr) {
/* Unmap both the RAM block and the guard page */
- munmap(ptr, size + pagesize);
+ munmap(ptr, max_size + pagesize);
}
}
--
2.24.1
