c746ed724d
In certain emergency cases such as media failure or removal, UFS will initiate a forced unmount in order to prevent dirty buffers from accumulating against the no-longer-usable filesystem. The presence of a stacked filesystem such as nullfs or unionfs above the UFS mount will prevent this forced unmount from succeeding. This change addreses the situation by allowing stacked filesystems to be recursively unmounted on a taskqueue thread when the MNT_RECURSE flag is specified to dounmount(). This call will block until all upper mounts have been removed unless the caller specifies the MNT_DEFERRED flag to indicate the base filesystem should also be unmounted from the taskqueue. To achieve this, the recently-added vfs_pin_from_vp()/vfs_unpin() KPIs have been combined with the existing 'mnt_uppers' list used by nullfs and renamed to vfs_register_upper_from_vp()/vfs_unregister_upper(). The format of the mnt_uppers list has also been changed to accommodate filesystems such as unionfs in which a given mount may be stacked atop more than one lower mount. Additionally, management of lower FS reclaim/unlink notifications has been split into a separate list managed by a separate set of KPIs, as registration of an upper FS no longer implies interest in these notifications. Reviewed by: kib, mckusick Tested by: pho Differential Revision: https://reviews.freebsd.org/D31016 |
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| .. | ||
| union_subr.c | ||
| union_vfsops.c | ||
| union_vnops.c | ||
| union.h | ||