Re: nonblocking I/O - testing whether file has more data to read

If there's a version of FAM available for your target OS you might look into SGI::FAM which sits on top of the fam(3X) routines and has shims in the kernel notify a userland daemon when specified files are changed (and the daemon then passes that info back to your program).

Comment on Re: nonblocking I/O - testing whether file has more data to read

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Re: Re: nonblocking I/O - testing whether file has more data to read by hv (Prior) on Apr 08, 2004 at 22:32 UTC
Interesting - I noticed this in `/usr/include/bits/fcntl.h` the other day (as one does), and wondered whether any of them might be useful: `#ifdef __USE_GNU # define F_SETLEASE 1024 /* Set a lease. / # define F_GETLEASE 1025 / Enquire what lease is active. / # define F_NOTIFY 1026 / Request notfications on a directory. * +/ #endif` [download] Prompted by your suggestion, I found that these are actually documented in more recent versions of the `fcntl(2)` manpage than I have, such as in this HTML version. Unfortunately it notifies only of processes opening or truncating a file, and you have to be the owner of the file (or root), which means it isn't very useful for my current needs. I see also that there is a fam rpm for my O/S - but while I wasn't able to Google any docs on how to use it, I did find a number of threads about how insecure it was (due to its dependency on portmapper), which makes me reluctant to try it. Hugo	[reply] [d/l] [select]

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Re: Re: nonblocking I/O - testing whether file has more data to read
by hv (Prior) on Apr 08, 2004 at 22:32 UTC

Interesting - I noticed this in /usr/include/bits/fcntl.h the other day (as one does), and wondered whether any of them might be useful:

#ifdef __USE_GNU
# define F_SETLEASE 1024    /* Set a lease.  */
# define F_GETLEASE 1025    /* Enquire what lease is active.  */
# define F_NOTIFY   1026    /* Request notfications on a directory.  *
+/
#endif
[download]

Prompted by your suggestion, I found that these are actually documented in more recent versions of the fcntl(2) manpage than I have, such as in this HTML version.

Unfortunately it notifies only of processes opening or truncating a file, and you have to be the owner of the file (or root), which means it isn't very useful for my current needs.

I see also that there is a fam rpm for my O/S - but while I wasn't able to Google any docs on how to use it, I did find a number of threads about how insecure it was (due to its dependency on portmapper), which makes me reluctant to try it.

Hugo

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