Re: inotify?

[Kevin Connor Arpe <kevinarpe@gmail.com>]

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Hi,

Sorry, I am a GMail user, so I am unable to reply to the original email
from Eric Blake eblake@redhat.com on Thu May 3 14:03:00 GMT 2018:
https://cygwin.com/pipermail/cygwin/2018-May/237069.html

Eric wrote: <<And patches to make Cygwin support inotify_init() and
friends implemented
on top of the Windows native API are certainly welcome.>>

First, please correct me if Linux-style inotify is already supported in
Cygwin.  As I understand, it is not.  To be clear, when I say "inotify", I
mean this Linux kernel API:
https://man7.org/linux/man-pages/man7/inotify.7.html

Second, I am interested in exploring this feature as a personal project.
After some research, I found two different solutions on Windows:

   1. FindNextChangeNotification() and friends explained here:
   https://learn.microsoft.com/en-us/windows/win32/fileio/obtaining-directory-change-notifications
   2. (NTFS) Change Journals explained here:
   https://learn.microsoft.com/en-us/windows/win32/fileio/change-journals

There is some discussion about both approaches on StackOverflow.com here:
https://stackoverflow.com/questions/3517460/is-there-anything-like-inotify-on-windows

In short, it sounds like #1 (above) is unreliable and can drop/miss file
system events if too fast and/or the kernel notification queue is
full/overloaded.

However, #2 (above) requires journalling to be enabled on an NTFS volume.
And, it sounds like this feature is *only* available on NTFS volumes.
(FAT/32 & friends would need to use #1.)

My thoughts & concerns:

   - #1 might be easier to program but if dropped events are a reality,
   then ... meh, not such a great feature!
   - #2 is restricted to NTFS, but sounds very reliable ("rock solid", one
   person said).  However, journalling needs to be enabled.  I guess the
   inotify API can just return an error if journaling is disabled for an NTFS
   volume.  And, I see two solutions for non-NTFS volumes: inotify API returns
   error, or fall-back to #2.

More: It sounds like journaling might be disabled by default.

   -
   https://stackoverflow.com/questions/27184283/is-the-usn-journal-disabled-by-default
   - https://devblogs.microsoft.com/oldnewthing/20130101-00/?p=5673

And enabling probably requires local admin access.  Maybe some kind of flag
can choose #1 or #2?

I would appreciate it if people could share their thoughts and advice.

The Linux inotify API is an excellent feature.  I have used it a few times
with great success.  It would be nice to have this feature on Cygwin.

Kind regards,
Kevin ARPE
Tokyo, Japan
https://github.com/kevinarpe