dillon c55dc89c34 Add vfs.enable_userblk_io sysctl to control whether user reads and writes ... to buffered block devices are allowed. The default is to be backwards compatible, i.e. reads and writes are allowed. The idea is for a larger crowd to start running with this disabled and see what problems, if any, crop up, and then to change the default to off and see if any problems crop up in the next 6 months prior to potentially removing support entirely. There are still a few people, Julian and myself included, who believe the buffered block device access from usermode to be useful. Remove use of vnode->v_lastr from buffered block device I/O in preparation for removal of vnode->v_lastr field, replacing it with the already existing seqcount metric to detect sequential operation. Reviewed by: Alan Cox <alc@cs.rice.edu>, David Greenman <dg@root.com>		1999-09-17 06:10:27 +00:00
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spec_vnops.c	Add vfs.enable_userblk_io sysctl to control whether user reads and writes	1999-09-17 06:10:27 +00:00