Date: Sat, 13 Aug 2022 09:51:32 -0700 From: Craig Leres <leres@freebsd.org> To: meator <meator.dev@gmail.com>, freebsd-hackers@FreeBSD.org Subject: Re: How to monitor a directory in FreeBSD? Message-ID: <754a7f6d-8fbe-aae0-796b-e5c0e782fc4f@freebsd.org> In-Reply-To: <652f3c12-388c-04d0-ebeb-753b76b2b742@gmail.com> References: <652f3c12-388c-04d0-ebeb-753b76b2b742@gmail.com>
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On 8/13/22 05:16, meator wrote: > Hello. I'm working on a C program that needs to know whether files and > directories in a specific directory were added, modified or deleted. (It > should also be done recursively for all subdirectories, but to keep it > simple I don't take recursion into account. It shouldn't be that hard to > implement it after I will be able to monitor a directory nonrecursively.) > > I don't have much experience with BSD programming but I know POSIX. I > have used inotify before for this purpose, but BSD doesn't have it so I > started looking for BSD alternatives. The internet lead me to kqueue. I > saw some criticism of it, but I don't need to monitor several thousands > of files, so I hope it will be usable for my use case. > > The EVFILT_VNODE filter documentation in kqueue(2) doesn't really talk > about files and directories, it talks about file descriptors. Inotify on > the other hand is very explicit about handling files in the monitored > directory. Kqueue can still detect creation and deletion of files inside > the monitored directory with NOTE_WRITE for files and NOTE_LINK for > directories (at least I think, I made a little test program to test this). > > This is useful, but I don't see any obvious way to identify a newly > created file inside the monitored directory. File creation would result > in NOTE_WRITE, but struct kevent doesn't have any "name" field (unlike > inotify) that would show which file was created. I would have to make a > list of directories and compare the old state with the current state to > see the file which was added. > > Kqueue also doesn't seem to detect modification of files inside the > monitored directory. Does this mean that I would have to monitor every > single file in the directory to make this work? > > I think this shows that kqueue isn't really meant to be used for > monitoring directory members. Is this true? Have I misunderstood something? The way I've done it is is to use EVFILT_VNODE/NOTE_WRITE to tell me when the directory has changed and then roll my own opendir()/readdir() code to detect what (if anything) was added or deleted. Craig
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