Re: inotify?

Re: inotify?

[Kevin Connor Arpe]

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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

Re: inotify?

[Ken Brown]

On 10/6/2022 12:29 PM, Kevin Connor Arpe wrote:
> 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.

That's correct.

[...]

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

I don't know if this will help, but Emacs has a filenotify feature which, on 
Linux, is based on inotify.  In the native Windows build of Emacs, filenotify is 
implemented in the file src/w32notify.c in the Emacs source tree.  Looking at 
how this is done might give you some ideas.

> 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.

Agreed.  Good luck.

Ken

Re: inotify?

[Kevin Connor Arpe]

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Ken,

Sorry for my late reply.  Your hint to read the Emacs source code was
incredibly helpful.
This line:
https://github.com/jwiegley/emacs-release/blob/master/src/w32notify.c#L255
calls ReadDirectoryChangesW().
Reading the Win32 API docs very closely, I discovered that I can pass a
large(r) buffer to this function.  This can greatly reduce the chance of
lost events.
(Oddly, in *all* code samples that I found, all of them used relatively
small buffers.  Even the Emacs code uses a tiny 16kb buffer.)
I wrote a test driver for ReadDirectoryChangesW() to better understand
the API.
I did some analysis to map the Linux API to Win32 capabilities.  As
expected, there isn't a perfect 1:1 match, but there is significant overlap
-- enough (IMHO) to make inotify useful on Cygwin.
I also started reading the Cygwin source code.  It seems possible to impl
inotify functionality by creating a new subclass of fhandler_base, e.g.,
fhandler_inotify.

I will reply to this thread when/if I have questions in the future.

Thanks,
Arpe

On Fri, Oct 7, 2022 at 4:59 AM Ken Brown <kbrown@cornell.edu> wrote:

> On 10/6/2022 12:29 PM, Kevin Connor Arpe wrote:
> > 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.
>
> That's correct.
>
> [...]
>
> > I would appreciate it if people could share their thoughts and advice.
>
> I don't know if this will help, but Emacs has a filenotify feature which,
> on
> Linux, is based on inotify.  In the native Windows build of Emacs,
> filenotify is
> implemented in the file src/w32notify.c in the Emacs source tree.  Looking
> at
> how this is done might give you some ideas.
>
> > 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.
>
> Agreed.  Good luck.
>
> Ken
>
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Re: inotify?

[Ulli Horlacher]

On Thu 2018-05-03 (11:36), Richard H Lee wrote:
> On 03/05/2018 10:35, Ulli Horlacher wrote:
> 
> > Is there a similar service "tell me of new files in this directory tree"
> > in Windows which I can use instead?
> 
> Windows does have its own file and directory watching API.

How can I use it via bash or perl?


-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK         
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    http://www.tik.uni-stuttgart.de/
REF:<3fd715eb-7048-c0bf-c82d-8ed5d7c508cb@gmail.com>

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Re: inotify?

[Eric Blake]

On 05/03/2018 05:36 AM, Richard H Lee wrote:
> On 03/05/2018 10:35, Ulli Horlacher wrote:
>> Is there a similar service "tell me of new files in this directory tree"
>> in Windows which I can use instead?
> Windows does have its own file and directory watching API.

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

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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Re: inotify?

[Richard H Lee]

On 03/05/2018 10:35, Ulli Horlacher wrote:
> Is there a similar service "tell me of new files in this directory tree"
> in Windows which I can use instead?
Windows does have its own file and directory watching API.

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inotify?

[Ulli Horlacher]

I have written a program, which uses inotify(wait) to send new created or
modified files.
Since inotify is a Linux kernel service, my program does not run with
Cygwin.
Is there a similar service "tell me of new files in this directory tree" 
in Windows which I can use instead?

-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK         
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    http://www.tik.uni-stuttgart.de/
REF:<20180503093514.GA31178@rus.uni-stuttgart.de>

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