with a new implementation that has a mostly reentrant "addchar" routine, supports multiple message buffers in the kernel, and hides the implementation details from callers. The new code uses a kind of sequence number to represend the current read and write positions in the buffer. This approach (suggested mainly by bde) permits the read and write pointers to be maintained separately, which reduces the number of atomic operations that are required. The "mostly reentrant" above refers to the way that while it is now always safe to have any number of concurrent writers, readers could see the message buffer after a writer has advanced the pointers but before it has witten the new character. Discussed on: freebsd-arch |
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dmesg.8 | ||
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Makefile |