[src/trunk]: src/sys/dev/dkwedge Handle read-only parent devices.

[mlelstv <mlelstv%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/6141cf208d50
branches:  trunk
changeset: 379238:6141cf208d50
user:      mlelstv <mlelstv%NetBSD.org@localhost>
date:      Sat May 22 13:43:50 2021 +0000

description:
Handle read-only parent devices.

Currently this only affects xbd(4). Other disk drivers succeed opening
read-only disks as read-write and only fail subsequent write requests.

diffstat:

 sys/dev/dkwedge/dk.c |  25 +++++++++++++++++++++----
 1 files changed, 21 insertions(+), 4 deletions(-)

diffs (72 lines):

diff -r 1138b827d350 -r 6141cf208d50 sys/dev/dkwedge/dk.c
--- a/sys/dev/dkwedge/dk.c      Sat May 22 01:24:27 2021 +0000
+++ b/sys/dev/dkwedge/dk.c      Sat May 22 13:43:50 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: dk.c,v 1.102 2020/10/06 15:05:54 mlelstv Exp $ */
+/*     $NetBSD: dk.c,v 1.103 2021/05/22 13:43:50 mlelstv Exp $ */
 
 /*-
  * Copyright (c) 2004, 2005, 2006, 2007 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: dk.c,v 1.102 2020/10/06 15:05:54 mlelstv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: dk.c,v 1.103 2021/05/22 13:43:50 mlelstv Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_dkwedge.h"
@@ -90,6 +90,7 @@ struct dkwedge_softc {
        kcondvar_t      sc_dkdrn;
        u_int           sc_iopend;      /* I/Os pending */
        int             sc_flags;       /* flags (sc_iolock) */
+       int             sc_mode;        /* parent open mode */
 };
 
 #define        DK_F_WAIT_DRAIN         0x0001  /* waiting for I/O to drain */
@@ -1138,6 +1139,7 @@ dkopen(dev_t dev, int flags, int fmt, st
        struct dkwedge_softc *sc = dkwedge_lookup(dev);
        struct vnode *vp;
        int error = 0;
+       int mode;
 
        if (sc == NULL)
                return (ENODEV);
@@ -1155,12 +1157,27 @@ dkopen(dev_t dev, int flags, int fmt, st
        if (sc->sc_dk.dk_openmask == 0) {
                if (sc->sc_parent->dk_rawopens == 0) {
                        KASSERT(sc->sc_parent->dk_rawvp == NULL);
-                       error = dk_open_parent(sc->sc_pdev, FREAD | FWRITE, &vp);
+                       /*
+                        * Try open read-write. If this fails for EROFS
+                        * and wedge is read-only, retry to open read-only.
+                        */
+                       mode = FREAD | FWRITE;
+                       error = dk_open_parent(sc->sc_pdev, mode, &vp);
+                       if (error == EROFS && (flags & FWRITE) == 0) {
+                               mode &= ~FWRITE;
+                               error = dk_open_parent(sc->sc_pdev, mode, &vp);
+                       }
                        if (error)
                                goto popen_fail;
+                       /* remember open mode */
+                       sc->sc_mode = mode;
                        sc->sc_parent->dk_rawvp = vp;
                }
                sc->sc_parent->dk_rawopens++;
+       } else if (flags & ~sc->sc_mode & FWRITE) {
+               /* parent is opened read-only, cannot open read-write */
+               error = EROFS;
+               goto popen_fail;
        }
        if (fmt == S_IFCHR)
                sc->sc_dk.dk_copenmask |= 1;
@@ -1197,7 +1214,7 @@ dklastclose(struct dkwedge_softc *sc)
        mutex_exit(&sc->sc_dk.dk_openlock);
 
        if (vp) {
-               dk_close_parent(vp, FREAD | FWRITE);
+               dk_close_parent(vp, sc->sc_mode);
        }
 
        return error;