Follow up on my own post...
My intention is to perform file locking on remote volumes, including
AFPFS volumes. So far, I've found no documentation on how to implement
"AFP-style" mandatory locking using fcntl().
Then I remember that, while deprecated, the now-ancient FS API is still
around. Plan B was born: use FSOpenFork's deny-read & deny-write
permissions to implement file locking, then turn around and use open(2)
to access the data.
That didn't work. As soon as I opened the file via FSOpenFork, open(2)
would fail with "resource not available" error.
Hmm, that sounds exactly like what happens when open(2) tries to open a
file that has been opened by another process with O_SHLOCK or O_EXLOCK.
So it would appear that, rather than being completely different file
locking mechanisms, FSOpenFork() bridges to the advisory locking
provided by open(2). And when I rewrite my test code to use open(2)
O_SHLOCK and O_EXLOCK to access the same AFPFS volume from two different
clients, it works perfectly!
Now I'm wondering why the AFPFS volume (this on a Time Capsule, by the
way) reports VOL_CAP_INT_FLOCK=NO and VOL_CAP_INT_ADVLOCK=NO. The
functionality of open(2) on that volume would appear to directly
contradict that capability test.
Can anyone explain this?
Thanks!
James
James Bucanek <mailto:subscri...@gloaming.com>
February 26, 2018 at 1:11 PM
More annoying questions...
How does one use "AFP-style mandatory file locking" in macOS
(10.9...current)?
I'm trying to implement file locking/coordination across various
filesystems and servers.
The man page for getattrlist() includes the following filesystem
capability test:
VOL_CAP_INT_MANLOCK If this bit is set, the volume format implementation
supports AFP-style mandatory byte range locks
via ioctl(2).
AFPFS (a.k.a. AppleShare) volumes, particularly those on AirPort
Extreme / Time Capsule devices, return 1 for this capability. These
volumes do not support flock() or fcntl(F_SETLK) style advisory locking.
I looked at the man page for ioctl(2) and it contains no real
information. It says the commands for ioctl(2) are documented in
<sys/ioctl.h>.
So I had a look at <sys/ioctl.h> and found very little there; it's
basically an umbrella header for several other headers. So I went
through them one at a time: <sys/ttycom.h>, <sys/ioccom.h>,
<sys/filio.h> (the one I would have assumed it would be in), and
<sys/sockio.h>. I could found no mention of any kind of file or byte
range locking commands defined.
So, is it possible to lock files/ranges on an AFPFS volume using
ioctl(2), and if so where are these commands defined?
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Filesystem-dev mailing list (Filesystem-dev@lists.apple.com)
Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/filesystem-dev/subscriber%40gloaming.com
This email sent to subscri...@gloaming.com
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Filesystem-dev mailing list (Filesystem-dev@lists.apple.com)
Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/filesystem-dev/archive%40mail-archive.com
This email sent to arch...@mail-archive.com
