Re: non-persistant storage?
Hi Ulli,
On Dec 12 13:00, Ulli Horlacher wrote:
> I need to store some data (a few kB) non-persistant.
> On a real UNIX I would use /var/run, because after a shutdown all its
> content is lost.
> But on cygwin /var/run is stored on disk.
>
> I cannot use an environment variable, because different processes need to
> read/write the data.
>
> /proc is non-persistant (in respect to a reboot), but It is not a generic
> storage place.
>
> What can I use with cygwin instead?
>
> Installing third party software is not an option, it must work with a
> standard Windows (and cygwin).
Cygwin is just a user space DLL, it's not an OS. Creating RAM disk-like
storage is the job of the OS or an OS driver. Unfortunately, there's no
onboard RAM disk driver in Windows, just zillions of third-party solutions.
I see two options:
- Use XSI shared memory, as outlined in this thread already, or
- If you have the executables under source control, you can use
an O_TMPFILE on /dev/shm, and fork the worker process from there,
i.e.
fd = open ("/dev/shm", O_TMPFILE | O_RDWR, S_IRUSR | S_IWUSR);
if (fd >= 0)
{
write (fd, your_key, strlen (your_key));
switch (fork ())
{
case 0: /* child */
/* Use fd as you see fit */
break;
case -1: /* error */
default: /* parent */
close (fd);
wait (&status);
break;
}
}
Corinna
--
Corinna Vinschen
Cygwin Maintainer
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Re: non-persistant storage?
On Thu 2019-12-12 (17:06), L A Walsh wrote: > On 2019/12/12 13:40, Eliot Moss wrote: > > > Ah! I think what you want is a tmpfs or ramfs. > > Not sure if cygwin supports that ... > > > > Easiest thing might be to use /dev/shm. I used it during > development to store intermediate data that was later to be > transfered via a fifo... > > Basically check for existence of "/dev/shm" (exists on my cygwin). > if "tmp" didn't already exist, create it w/options similar to > /tmp (only owner can delete/edit): > > mkdir -m 1777 /tmp/shm/tmp > > > **Warning, "writes" to /dev/shm/tmp (or /dev/mem) can fill up > your system's memory, so its only good for "small files" > (small being well under your system's free memory amount). This is true for Linux, but not for cygwin, where /dev/shm is ntfs on disk: ~: uname -a CYGWIN_NT-10.0 VD-TIK-12 3.0.7(0.338/5/3) 2019-04-30 18:08 x86_64 Cygwin ~: df -TH /dev/shm Filesystem Type Size Used Avail Use% Mounted on C:/cygwin64ntfs 34G 25G 8.9G 74% / Its content is still there after a reboot and I can see it with the windows explorer: https://fex.belwue.de/fop/dyQzlG1x/X-20191213103905.png -- Ullrich Horlacher Server und Virtualisierung Rechenzentrum TIK Universitaet Stuttgart E-Mail: horlac...@tik.uni-stuttgart.de Allmandring 30aTel:++49-711-68565868 70569 Stuttgart (Germany) WWW:http://www.tik.uni-stuttgart.de/ REF:<5df2e42a.7020...@tlinx.org> -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
Re: non-persistant storage?
On 2019/12/12 22:26, Brian Inglis wrote: I've been using /run, with /var/run as a symlink to that, created in a permanent postinstall script /etc/postinstall/zp_mk_run_var_links.dash (with some others), for some time. It's currently using ~28KB. Is it feasible to mount /run on say /dev/shm/run and create and use files there? I don't see why you would need to change what you are doing unless your application whines about the symlink. I.e. VirtualBox didn't like me using a symlink in /opt to /home/opt on linux, so I mounted it w/a line in fstab. /home/opt /opt none rbind 0 0 Or would it be more feasible to use say Cyg/WinFUSE to provide that function? I don't know the state of cyg's support in those areas, so if you were forced to change, you'd get to do your own testing to see what worked, etc. I went one further under 'run' and 'tmp' -- I left those as public directories and put my UID or login name as my own directory under the common name. yeah 28k is nothing. I was using files measured in MBytes though the [server] system has over 100GB mem. The communication goes through unix-sockets, which also goes through /dev/shm, but its cleanup is technically the responsibility of the OS, so, if lucky -- it cleans it up, if not, no worse off than before. I don't run many OS progs on my Win machine cuz Win tended to flake out in running tasks and wouldn't say anything when it went wrong. So now, I just have a cronjobs on my linux server that use ssh to login to run jobs on windows... -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
Re: non-persistant storage?
On 2019-12-12 18:06, L A Walsh wrote: > On 2019/12/12 13:40, Eliot Moss wrote: >> Ah! I think what you want is a tmpfs or ramfs. >> Not sure if cygwin supports that ... >> > > Easiest thing might be to use /dev/shm. I used it during > development to store intermediate data that was later to be > transfered via a fifo... > > Basically check for existence of "/dev/shm" (exists on my cygwin). > if "tmp" didn't already exist, create it w/options similar to > /tmp (only owner can delete/edit): > > mkdir -m 1777 /tmp/shm/tmp > > > **Warning, "writes" to /dev/shm/tmp (or /dev/mem) can fill up > your system's memory, so its only good for "small files" > (small being well under your system's free memory amount). I've been using /run, with /var/run as a symlink to that, created in a permanent postinstall script /etc/postinstall/zp_mk_run_var_links.dash (with some others), for some time. It's currently using ~28KB. Is it feasible to mount /run on say /dev/shm/run and create and use files there? Or would it be more feasible to use say Cyg/WinFUSE to provide that function? -- Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada This email may be disturbing to some readers as it contains too much technical detail. Reader discretion is advised. -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
Re: non-persistant storage?
On 2019/12/12 13:40, Eliot Moss wrote: Ah! I think what you want is a tmpfs or ramfs. Not sure if cygwin supports that ... Easiest thing might be to use /dev/shm. I used it during development to store intermediate data that was later to be transfered via a fifo... Basically check for existence of "/dev/shm" (exists on my cygwin). if "tmp" didn't already exist, create it w/options similar to /tmp (only owner can delete/edit): mkdir -m 1777 /tmp/shm/tmp **Warning, "writes" to /dev/shm/tmp (or /dev/mem) can fill up your system's memory, so its only good for "small files" (small being well under your system's free memory amount). -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
Re: non-persistant storage?
Ah! I think what you want is a tmpfs or ramfs. Not sure if cygwin supports that ... Cheers - Eliot -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
Re: non-persistant storage?
On Thu 2019-12-12 (14:18), Eliot Moss wrote: > > I need to store some data (a few kB) non-persistant. > > On a real UNIX I would use /var/run, because after a shutdown all its > > content is lost. > > But on cygwin /var/run is stored on disk. > > > I would think of temp directories, such as /tmp. They can be cleaned out at > will > on restart, no? The data MUST be lost on shutdown (or power failure), not on reboot! Therefore it must be hold in memory, not on disk. -- Ullrich Horlacher Server und Virtualisierung Rechenzentrum TIK Universitaet Stuttgart E-Mail: horlac...@tik.uni-stuttgart.de Allmandring 30aTel:++49-711-68565868 70569 Stuttgart (Germany) WWW:http://www.tik.uni-stuttgart.de/ REF:<8905c7b6-b2e6-52bf-bcdd-66890db91...@cs.umass.edu> -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
Re: non-persistant storage?
On 12/12/2019 7:00 AM, Ulli Horlacher wrote: I need to store some data (a few kB) non-persistant. On a real UNIX I would use /var/run, because after a shutdown all its content is lost. But on cygwin /var/run is stored on disk. I cannot use an environment variable, because different processes need to read/write the data. /proc is non-persistant (in respect to a reboot), but It is not a generic storage place. What can I use with cygwin instead? Installing third party software is not an option, it must work with a standard Windows (and cygwin). I would think of temp directories, such as /tmp. They can be cleaned out at will on restart, no? Regards - Eliot -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
