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 <kwolf@redhat.com>
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@ -376,13 +376,21 @@ static void raw_probe_alignment(BlockDriverState *bs, int fd, Error **errp)
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}
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}
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static void raw_parse_flags(int bdrv_flags, int *open_flags)
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static void raw_parse_flags(int bdrv_flags, int *open_flags, bool has_writers)
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{
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bool read_write = false;
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assert(open_flags != NULL);
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*open_flags |= O_BINARY;
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*open_flags &= ~O_ACCMODE;
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if (bdrv_flags & BDRV_O_RDWR) {
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if (bdrv_flags & BDRV_O_AUTO_RDONLY) {
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read_write = has_writers;
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} else if (bdrv_flags & BDRV_O_RDWR) {
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read_write = true;
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}
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if (read_write) {
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*open_flags |= O_RDWR;
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} else {
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*open_flags |= O_RDONLY;
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@ -518,24 +526,12 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
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false);
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s->open_flags = open_flags;
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raw_parse_flags(bdrv_flags, &s->open_flags);
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raw_parse_flags(bdrv_flags, &s->open_flags, false);
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s->fd = -1;
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fd = qemu_open(filename, s->open_flags, 0644);
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ret = fd < 0 ? -errno : 0;
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if (ret == -EACCES || ret == -EROFS) {
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/* Try to degrade to read-only, but if it doesn't work, still use the
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* normal error message. */
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if (bdrv_apply_auto_read_only(bs, NULL, NULL) == 0) {
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bdrv_flags &= ~BDRV_O_RDWR;
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raw_parse_flags(bdrv_flags, &s->open_flags);
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assert(!(s->open_flags & O_CREAT));
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fd = qemu_open(filename, s->open_flags);
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ret = fd < 0 ? -errno : 0;
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}
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}
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if (ret < 0) {
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error_setg_errno(errp, -ret, "Could not open '%s'", filename);
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if (ret == -EROFS) {
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@ -846,12 +842,14 @@ static int raw_handle_perm_lock(BlockDriverState *bs,
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}
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static int raw_reconfigure_getfd(BlockDriverState *bs, int flags,
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int *open_flags, bool force_dup,
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int *open_flags, uint64_t perm, bool force_dup,
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Error **errp)
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{
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BDRVRawState *s = bs->opaque;
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int fd = -1;
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int ret;
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bool has_writers = perm &
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(BLK_PERM_WRITE | BLK_PERM_WRITE_UNCHANGED | BLK_PERM_RESIZE);
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int fcntl_flags = O_APPEND | O_NONBLOCK;
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#ifdef O_NOATIME
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fcntl_flags |= O_NOATIME;
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@ -862,7 +860,7 @@ static int raw_reconfigure_getfd(BlockDriverState *bs, int flags,
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*open_flags |= O_NONBLOCK;
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}
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raw_parse_flags(flags, open_flags);
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raw_parse_flags(flags, open_flags, has_writers);
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#ifdef O_ASYNC
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/* Not all operating systems have O_ASYNC, and those that don't
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@ -942,7 +940,7 @@ static int raw_reopen_prepare(BDRVReopenState *state,
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qemu_opts_to_qdict(opts, state->options);
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rs->fd = raw_reconfigure_getfd(state->bs, state->flags, &rs->open_flags,
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true, &local_err);
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state->perm, true, &local_err);
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if (local_err) {
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error_propagate(errp, local_err);
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ret = -1;
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@ -2720,7 +2718,7 @@ static int raw_check_perm(BlockDriverState *bs, uint64_t perm, uint64_t shared,
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s->perm_change_fd = rs->fd;
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} else {
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/* We may need a new fd if auto-read-only switches the mode */
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ret = raw_reconfigure_getfd(bs, bs->open_flags, &open_flags,
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ret = raw_reconfigure_getfd(bs, bs->open_flags, &open_flags, perm,
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false, errp);
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if (ret < 0) {
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return ret;
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@ -22,12 +22,12 @@ NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only)
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NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only)
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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
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NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only)
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NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only)
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NODE_NAME: TEST_DIR/t.IMGFMT (file)
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NODE_NAME: TEST_DIR/t.IMGFMT (file)
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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
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NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only)
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NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only)
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NODE_NAME: TEST_DIR/t.IMGFMT (file)
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NODE_NAME: TEST_DIR/t.IMGFMT (file)
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=== -blockdev with read-write image: read-only/auto-read-only combinations ===
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@ -50,11 +50,11 @@ node0: TEST_DIR/t.IMGFMT (file, read-only)
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node0: TEST_DIR/t.IMGFMT (file, read-only)
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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
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node0: TEST_DIR/t.IMGFMT (file, read-only)
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node0: TEST_DIR/t.IMGFMT (file)
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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
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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
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node0: TEST_DIR/t.IMGFMT (file, read-only)
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node0: TEST_DIR/t.IMGFMT (file)
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QEMU_PROG: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=node0: Could not open 'TEST_DIR/t.IMGFMT': Permission denied
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=== Try commit to backing file with auto-read-only ===
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