cem 47701ffd1e buf: Add B_INVALONERR flag to discard data
Setting the B_INVALONERR flag before a synchronous write causes the buf
cache to forcibly invalidate contents if the write fails (BIO_ERROR).

This is intended to be used to allow layers above the buffer cache to make
more informed decisions about when discarding dirty buffers without
successful write is acceptable.

As a proof of concept, use in msdosfs to handle failures to mark the on-disk
'dirty' bit during rw mount or ro->rw update.

Extending this to other filesystems is left as future work.

PR:		210316
Reviewed by:	kib (with objections)
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D21539
2019-09-11 21:24:14 +00:00
..
2018-05-16 02:58:05 +00:00
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