Commit 23dece19 authored by Kevin Wolf's avatar Kevin Wolf
Browse files

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: default avatarKevin Wolf <kwolf@redhat.com>
parent 6ceabe6f

block/file-posix.c

+17 −19
Original line number Diff line number Diff line
@@ -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;

tests/qemu-iotests/232.out

+6 −6
Original line number Diff line number Diff line
@@ -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 ===