I'm thinking about sending the following questions about the new directory
notification feature to the linux-kernel mailing list, with the intent of
finding out what the plans are for directory notification and how that can
be applied to Fam development. I'm posting here first looking for comments,
additions, etc.
Brian
----------------
I have a few questions about the directory notification feature that was added
in -test9. I recently started contributing to the Fam/Imon project that SGI
released (http://oss.sgi.com/projects/fam). Fam is a combination library and
daemon which applications can use to monitor files on local and remote
filesystems, and Imon is a kernel driver used to notify Fam when a change has
been made. With the addition of directory notification into the main kernel,
it looks like the Imon portion has become obsolete, and Fam can now be reworked
to use it.
The questions are:
Are there any plans to increase the amount of data sent to the application,
either before or after 2.4.0? Imon currently provides the device and inode
of the file that changed. Without this, it looks like Fam will have to store
the state of the directories it is monitoring so it find out which file
actually changed. It looks like the options are increasing the size of the
siginfo_t struct, or using the void pointer parameter in the sa_sigaction
handler. I'm not seeing anything in the kernel which allows the use of the
latter though.
Are there any plans to implement file notification? Fam currently supports
the ability to monitor a single file. Having this support in the kernel
isn't that big a deal, Fam can easily monitor the directory and ignore
changes to the other files. There is also some concern about Fam running
out of file descriptors with applications which monitor lots of files, so it
is probably a good thing to go directory only anyway.
Currently, if the directory which is being monitored is deleted, no signal
is generated. Any plans to change this? It would be possible to have Fam
monitor the directory that the application is interested in along with its
parent, but this would require two file descriptors for each "monitored"
directory, cutting the number of directories Fam could monitor in half.
Any plans to back-port directory notification to 2.2.x?
I'm fairly new to kernel development, but I'm willing to help out with any
changes that may or may not be decided on.
Thanks for the time,
Brian
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