[Qemu-devel] [PATCH 1/4] qcow2: Make qcow2_cache_table_release() work only in Linux

[Alberto Garcia]

We are using QEMU_MADV_DONTNEED to discard the memory of individual L2
cache tables. The problem with this is that those semantics are
specific to the Linux madvise() system call. Other implementations of
madvise() (including the very Linux implementation of posix_madvise())
don't do that, so we cannot use them for the same purpose.

This patch makes the code Linux-specific and uses madvise() directly
since there's no point in going through qemu_madvise() for this.

Signed-off-by: Alberto Garcia <address@hidden>
---
 block/qcow2-cache.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
index 6eaefed..ab8ee2d 100644
--- a/block/qcow2-cache.c
+++ b/block/qcow2-cache.c
@@ -66,7 +66,8 @@ static inline int qcow2_cache_get_table_idx(BlockDriverState 
*bs,
 static void qcow2_cache_table_release(BlockDriverState *bs, Qcow2Cache *c,
                                       int i, int num_tables)
 {
-#if QEMU_MADV_DONTNEED != QEMU_MADV_INVALID
+/* Using MADV_DONTNEED to discard memory is a Linux-specific feature */
+#ifdef CONFIG_LINUX
     BDRVQcow2State *s = bs->opaque;
     void *t = qcow2_cache_get_table_addr(bs, c, i);
     int align = getpagesize();
@@ -74,7 +75,7 @@ static void qcow2_cache_table_release(BlockDriverState *bs, 
Qcow2Cache *c,
     size_t offset = QEMU_ALIGN_UP((uintptr_t) t, align) - (uintptr_t) t;
     size_t length = QEMU_ALIGN_DOWN(mem_size - offset, align);
     if (length > 0) {
-        qemu_madvise((uint8_t *) t + offset, length, QEMU_MADV_DONTNEED);
+        madvise((uint8_t *) t + offset, length, MADV_DONTNEED);
     }
 #endif
 }
-- 
2.10.2