From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43297) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f94NJ-0004wI-DP for qemu-devel@nongnu.org; Thu, 19 Apr 2018 03:53:02 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f94NG-0002x0-9d for qemu-devel@nongnu.org; Thu, 19 Apr 2018 03:53:01 -0400 From: Stefan Hajnoczi Date: Thu, 19 Apr 2018 15:52:32 +0800 Message-Id: <20180419075232.31407-3-stefanha@redhat.com> In-Reply-To: <20180419075232.31407-1-stefanha@redhat.com> References: <20180419075232.31407-1-stefanha@redhat.com> Subject: [Qemu-devel] [RFC 2/2] block/file-posix: verify page cache is not used List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Max Reitz , Kevin Wolf , Sergio Lopez , qemu-block@nongnu.org, "Dr. David Alan Gilbert" , Stefan Hajnoczi 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 --- 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