From 23dece19da41724349809873923e20a48b619cb7 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Fri, 1 Mar 2019 22:15:11 +0100 Subject: [PATCH] file-posix: Make auto-read-only dynamic Until now, with auto-read-only=on we tried to open the file read-write first and if that failed, read-only was tried. This is actually not good enough for libvirt, which gives QEMU SELinux permissions for read-write only as soon as it actually intends to write to the image. So we need to be able to switch between read-only and read-write at runtime. This patch makes auto-read-only dynamic, i.e. the file is opened read-only as long as no user of the node has requested write permissions, but it is automatically reopened read-write as soon as the first writer is attached. Conversely, if the last writer goes away, the file is reopened read-only again. bs->read_only is no longer set for auto-read-only=on files even if the file descriptor is opened read-only because it will be transparently upgraded as soon as a writer is attached. This changes the output of qemu-iotests 232. Signed-off-by: Kevin Wolf --- block/file-posix.c | 36 +++++++++++++++++------------------- tests/qemu-iotests/232.out | 12 ++++++------ 2 files changed, 23 insertions(+), 25 deletions(-) diff --git a/block/file-posix.c b/block/file-posix.c index e41e0779c6..d41059d139 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -376,13 +376,21 @@ static void raw_probe_alignment(BlockDriverState *bs, int fd, Error **errp) } } -static void raw_parse_flags(int bdrv_flags, int *open_flags) +static void raw_parse_flags(int bdrv_flags, int *open_flags, bool has_writers) { + bool read_write = false; assert(open_flags != NULL); *open_flags |= O_BINARY; *open_flags &= ~O_ACCMODE; - if (bdrv_flags & BDRV_O_RDWR) { + + if (bdrv_flags & BDRV_O_AUTO_RDONLY) { + read_write = has_writers; + } else if (bdrv_flags & BDRV_O_RDWR) { + read_write = true; + } + + if (read_write) { *open_flags |= O_RDWR; } else { *open_flags |= O_RDONLY; @@ -518,24 +526,12 @@ static int raw_open_common(BlockDriverState *bs, QDict *options, false); s->open_flags = open_flags; - raw_parse_flags(bdrv_flags, &s->open_flags); + raw_parse_flags(bdrv_flags, &s->open_flags, false); s->fd = -1; fd = qemu_open(filename, s->open_flags, 0644); ret = fd < 0 ? -errno : 0; - if (ret == -EACCES || ret == -EROFS) { - /* Try to degrade to read-only, but if it doesn't work, still use the - * normal error message. */ - if (bdrv_apply_auto_read_only(bs, NULL, NULL) == 0) { - bdrv_flags &= ~BDRV_O_RDWR; - raw_parse_flags(bdrv_flags, &s->open_flags); - assert(!(s->open_flags & O_CREAT)); - fd = qemu_open(filename, s->open_flags); - ret = fd < 0 ? -errno : 0; - } - } - if (ret < 0) { error_setg_errno(errp, -ret, "Could not open '%s'", filename); if (ret == -EROFS) { @@ -846,12 +842,14 @@ static int raw_handle_perm_lock(BlockDriverState *bs, } static int raw_reconfigure_getfd(BlockDriverState *bs, int flags, - int *open_flags, bool force_dup, + int *open_flags, uint64_t perm, bool force_dup, Error **errp) { BDRVRawState *s = bs->opaque; int fd = -1; int ret; + bool has_writers = perm & + (BLK_PERM_WRITE | BLK_PERM_WRITE_UNCHANGED | BLK_PERM_RESIZE); int fcntl_flags = O_APPEND | O_NONBLOCK; #ifdef O_NOATIME fcntl_flags |= O_NOATIME; @@ -862,7 +860,7 @@ static int raw_reconfigure_getfd(BlockDriverState *bs, int flags, *open_flags |= O_NONBLOCK; } - raw_parse_flags(flags, open_flags); + raw_parse_flags(flags, open_flags, has_writers); #ifdef O_ASYNC /* Not all operating systems have O_ASYNC, and those that don't @@ -942,7 +940,7 @@ static int raw_reopen_prepare(BDRVReopenState *state, qemu_opts_to_qdict(opts, state->options); rs->fd = raw_reconfigure_getfd(state->bs, state->flags, &rs->open_flags, - true, &local_err); + state->perm, true, &local_err); if (local_err) { error_propagate(errp, local_err); ret = -1; @@ -2720,7 +2718,7 @@ static int raw_check_perm(BlockDriverState *bs, uint64_t perm, uint64_t shared, s->perm_change_fd = rs->fd; } else { /* We may need a new fd if auto-read-only switches the mode */ - ret = raw_reconfigure_getfd(bs, bs->open_flags, &open_flags, + ret = raw_reconfigure_getfd(bs, bs->open_flags, &open_flags, perm, false, errp); if (ret < 0) { return ret; diff --git a/tests/qemu-iotests/232.out b/tests/qemu-iotests/232.out index 5036ef13d4..5bcc44bb62 100644 --- a/tests/qemu-iotests/232.out +++ b/tests/qemu-iotests/232.out @@ -22,12 +22,12 @@ NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only) NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only) QEMU_PROG: -drive driver=file,file=TEST_DIR/t.IMGFMT,if=none,read-only=off,auto-read-only=off: Could not open 'TEST_DIR/t.IMGFMT': Permission denied -NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only) -NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only) +NODE_NAME: TEST_DIR/t.IMGFMT (file) +NODE_NAME: TEST_DIR/t.IMGFMT (file) QEMU_PROG: -drive driver=file,file=TEST_DIR/t.IMGFMT,if=none,auto-read-only=off: Could not open 'TEST_DIR/t.IMGFMT': Permission denied -NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only) -NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only) +NODE_NAME: TEST_DIR/t.IMGFMT (file) +NODE_NAME: TEST_DIR/t.IMGFMT (file) === -blockdev with read-write image: read-only/auto-read-only combinations === @@ -50,11 +50,11 @@ node0: TEST_DIR/t.IMGFMT (file, read-only) node0: TEST_DIR/t.IMGFMT (file, read-only) QEMU_PROG: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=node0,read-only=off,auto-read-only=off: Could not open 'TEST_DIR/t.IMGFMT': Permission denied -node0: TEST_DIR/t.IMGFMT (file, read-only) +node0: TEST_DIR/t.IMGFMT (file) QEMU_PROG: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=node0,read-only=off: Could not open 'TEST_DIR/t.IMGFMT': Permission denied QEMU_PROG: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=node0,auto-read-only=off: Could not open 'TEST_DIR/t.IMGFMT': Permission denied -node0: TEST_DIR/t.IMGFMT (file, read-only) +node0: TEST_DIR/t.IMGFMT (file) QEMU_PROG: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=node0: Could not open 'TEST_DIR/t.IMGFMT': Permission denied === Try commit to backing file with auto-read-only ===