| Message ID | 20190730145727.28965-2-kwolf@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | fdc: Fix inserting read-only media in empty drive | expand |
On 30.07.19 16:57, Kevin Wolf wrote: > In order to insert a read-only medium (i.e. a read-only block node) to > the BlockBackend of a floppy drive, we must not have taken write > permissions on that BlockBackend, or the operation will fail with the > error message "Block node is read-only". > > The device already takes care to remove all permissions when the medium > is ejected, but the state isn't correct if the drive is initially empty: > It uses blk_is_read_only() to check whether write permissions should be > taken, but this function returns false for empty BlockBackends in the > common case. > > Fix floppy_drive_realize() to avoid taking write permissions if the > drive is empty. ...and once the drive is loaded with anything, fd_change_cb() calls blkconf_apply_backend_option() again with the updated RO state. Looks correct. > Signed-off-by: Kevin Wolf <kwolf@redhat.com> > --- > hw/block/fdc.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) Reviewed-by: Max Reitz <mreitz@redhat.com>
On 7/30/19 10:57 AM, Kevin Wolf wrote: > In order to insert a read-only medium (i.e. a read-only block node) to > the BlockBackend of a floppy drive, we must not have taken write > permissions on that BlockBackend, or the operation will fail with the > error message "Block node is read-only". > > The device already takes care to remove all permissions when the medium > is ejected, but the state isn't correct if the drive is initially empty: > It uses blk_is_read_only() to check whether write permissions should be > taken, but this function returns false for empty BlockBackends in the > common case. > > Fix floppy_drive_realize() to avoid taking write permissions if the > drive is empty. > > Signed-off-by: Kevin Wolf <kwolf@redhat.com> > --- > hw/block/fdc.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/hw/block/fdc.c b/hw/block/fdc.c > index 77af9979de..9b24cb9b85 100644 > --- a/hw/block/fdc.c > +++ b/hw/block/fdc.c > @@ -514,6 +514,7 @@ static void floppy_drive_realize(DeviceState *qdev, Error **errp) > FloppyDrive *dev = FLOPPY_DRIVE(qdev); > FloppyBus *bus = FLOPPY_BUS(qdev->parent_bus); > FDrive *drive; > + bool read_only; > int ret; > > if (dev->unit == -1) { > @@ -542,6 +543,12 @@ static void floppy_drive_realize(DeviceState *qdev, Error **errp) > dev->conf.blk = blk_new(qemu_get_aio_context(), 0, BLK_PERM_ALL); > ret = blk_attach_dev(dev->conf.blk, qdev); > assert(ret == 0); > + > + /* Don't take write permissions on an empty drive to allow attaching a > + * read-only node later */ > + read_only = true; > + } else { > + read_only = !blk_bs(dev->conf.blk) || blk_is_read_only(dev->conf.blk); > } > > blkconf_blocksizes(&dev->conf); > @@ -559,9 +566,7 @@ static void floppy_drive_realize(DeviceState *qdev, Error **errp) > dev->conf.rerror = BLOCKDEV_ON_ERROR_AUTO; > dev->conf.werror = BLOCKDEV_ON_ERROR_AUTO; > > - if (!blkconf_apply_backend_options(&dev->conf, > - blk_is_read_only(dev->conf.blk), > - false, errp)) { > + if (!blkconf_apply_backend_options(&dev->conf, read_only, false, errp)) { > return; > } > > Smells correct. Reviewed-by: John Snow <jsnow@redhat.com>
diff --git a/hw/block/fdc.c b/hw/block/fdc.c index 77af9979de..9b24cb9b85 100644 --- a/hw/block/fdc.c +++ b/hw/block/fdc.c @@ -514,6 +514,7 @@ static void floppy_drive_realize(DeviceState *qdev, Error **errp) FloppyDrive *dev = FLOPPY_DRIVE(qdev); FloppyBus *bus = FLOPPY_BUS(qdev->parent_bus); FDrive *drive; + bool read_only; int ret; if (dev->unit == -1) { @@ -542,6 +543,12 @@ static void floppy_drive_realize(DeviceState *qdev, Error **errp) dev->conf.blk = blk_new(qemu_get_aio_context(), 0, BLK_PERM_ALL); ret = blk_attach_dev(dev->conf.blk, qdev); assert(ret == 0); + + /* Don't take write permissions on an empty drive to allow attaching a + * read-only node later */ + read_only = true; + } else { + read_only = !blk_bs(dev->conf.blk) || blk_is_read_only(dev->conf.blk); } blkconf_blocksizes(&dev->conf); @@ -559,9 +566,7 @@ static void floppy_drive_realize(DeviceState *qdev, Error **errp) dev->conf.rerror = BLOCKDEV_ON_ERROR_AUTO; dev->conf.werror = BLOCKDEV_ON_ERROR_AUTO; - if (!blkconf_apply_backend_options(&dev->conf, - blk_is_read_only(dev->conf.blk), - false, errp)) { + if (!blkconf_apply_backend_options(&dev->conf, read_only, false, errp)) { return; }
In order to insert a read-only medium (i.e. a read-only block node) to the BlockBackend of a floppy drive, we must not have taken write permissions on that BlockBackend, or the operation will fail with the error message "Block node is read-only". The device already takes care to remove all permissions when the medium is ejected, but the state isn't correct if the drive is initially empty: It uses blk_is_read_only() to check whether write permissions should be taken, but this function returns false for empty BlockBackends in the common case. Fix floppy_drive_realize() to avoid taking write permissions if the drive is empty. Signed-off-by: Kevin Wolf <kwolf@redhat.com> --- hw/block/fdc.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)