Re: Impact of having a large number of open file descriptors

Ivan Voras wrote:
Im thinking again of the old idea of implementing poor man's file
replication system using kqueue to monitor changes on files.

It would be cool to have a kernel interface so you could
attach to a mountpoint and receive a log of all activity
on that file system. That's similar to what DragonFly's
journaling feature does.

Unfortunately the kqueue interface isn't capable of doing
something like that ... So this is not an answer to your
question, I'm afraid.

One other question: do kqueue events "coalesce" in the sense that if N
operations happen (like write()s), there can be < N events passed to the
kqueue (NOTE_WRITE)?

The manpage says: "Multiple events which trigger the filter
do not result in multiple kevents being placed on the kqueue;
instead, the filter will aggregate the events into a single
struct kevent."

While at it, will EVFILT_VNODE and NOTE_WRITE catch "additional" ways
the file can be modified, meaning mmap()?

A quick grep for NOTE_WRITE on the sys tree indicates that
it doesn't. I'm not 100% sure though.

Best regards
Oliver

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