This commit is for debugging only. Do not merge it. mincore(2) checks whether pages are resident. Use it to verify that page cache has been dropped.
You can trigger a verification failure by mmapping the image file from another process and loading a byte from a page so that it becomes resident. bdrv_co_invalidate_cache() will fail while the process is alive. Signed-off-by: Stefan Hajnoczi <[email protected]> --- block/file-posix.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 71 insertions(+) diff --git a/block/file-posix.c b/block/file-posix.c index df4f52919f..d3105269c6 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -2236,6 +2236,75 @@ static int coroutine_fn raw_co_block_status(BlockDriverState *bs, return ret | BDRV_BLOCK_OFFSET_VALID; } +static bool is_mincore(void *addr, size_t length) +{ + size_t vec_len = DIV_ROUND_UP(length, sysconf(_SC_PAGESIZE)); + unsigned char *vec; + size_t i; + int ret; + bool incore = false; + + vec = g_malloc(vec_len); + ret = mincore(addr, length, vec); + if (ret < 0) { + incore = true; + goto out; + } + + for (i = 0; i < vec_len; i++) { + if (vec[i] & 0x1) { + incore = true; + break; + } + } + +out: + g_free(vec); + return incore; +} + +static void check_not_in_page_cache(BlockDriverState *bs, Error **errp) +{ + const size_t WINDOW_SIZE = 128 * 1024 * 1024; + BDRVRawState *s = bs->opaque; + void *window = NULL; + size_t length = 0; + off_t end; + off_t offset; + + end = raw_getlength(bs); + + for (offset = 0; offset < end; offset += WINDOW_SIZE) { + void *new_window; + size_t new_length = MIN(end - offset, WINDOW_SIZE); + + if (new_length != length) { + munmap(window, length); + window = NULL; + length = 0; + } + + new_window = mmap(window, new_length, PROT_NONE, MAP_PRIVATE, + s->fd, offset); + if (new_window == MAP_FAILED) { + error_setg_errno(errp, errno, "mmap failed"); + break; + } + + window = new_window; + length = new_length; + + if (is_mincore(window, length)) { + error_setg(errp, "page cache still in use!"); + break; + } + } + + if (window) { + munmap(window, length); + } +} + static void coroutine_fn raw_co_invalidate_cache(BlockDriverState *bs, Error **errp) { @@ -2270,6 +2339,8 @@ static void coroutine_fn raw_co_invalidate_cache(BlockDriverState *bs, return; } #endif /* __linux__ */ + + check_not_in_page_cache(bs, errp); } static coroutine_fn BlockAIOCB *raw_aio_pdiscard(BlockDriverState *bs, -- 2.14.3
