Re: Finding an available fss device

[Emmanuel Dreyfus <manu%netbsd.org@localhost>]

On Sat, Aug 11, 2018 at 10:52:42AM +0700, Robert Elz wrote:
> I doubt that your new proposed ioctl() is a very good
> interface 

Indeed, the following change is enough to find a free fss without a 
hang, and it does not introduce a new ioctl.  It is quite close to 
your proposal, except I lock before testing FSS_ACTIVE. Why would
test then lock? 

Index: sys/dev/fss.c
===================================================================
RCS file: /cvsroot/src/sys/dev/fss.c,v
retrieving revision 1.98.2.2
diff -U4 -r1.98.2.2 fss.c
--- sys/dev/fss.c       13 Jan 2018 05:38:54 -0000      1.98.2.2
+++ sys/dev/fss.c       12 Aug 2018 08:00:52 -0000
@@ -336,9 +336,13 @@
                fss->fss_csize = fss50->fss_csize;
                fss->fss_flags = 0;
                /* Fall through */
        case FSSIOCSET:
-               mutex_enter(&sc->sc_lock);
+               if (mutex_tryenter(&sc->sc_lock) == 0) {
+                       error = EBUSY;
+                       break;
+               }
+
                if ((flag & FWRITE) == 0)
                        error = EPERM;
                else if ((sc->sc_flags & FSS_ACTIVE) != 0)
                        error = EBUSY;



-- 
Emmanuel Dreyfus
manu%netbsd.org@localhost