mount.nfs: Refactor mount version and protocol autonegotiation

Clean up.

I'm beginning to agree with Bruce and Steve's assessment that the
fallthrough switch case in nfs_try_mount() is more difficult to read
and understand than it needs to be.  The logic that manages
negotiating NFS version and protocol settings is getting more complex
over time anyway.

So let's split the autonegotiation piece out of nfs_try_mount().

We can reduce indenting, and use cleaner switch-based logic.  Also,
adding more comments can only help.

Neil also suggested replacing the pre-call "errno = 0" trick.  The
lower-level functions may try to mount several times (given a list of
addresses to try).  errno could be set by any of those.  The mount
request will succeed at some point, and "success" is returned, but
errno is still set to some non-zero value.

The kernel version check in nfs_try_mount() is more or less loop
invariant: it's impossible for the result of that test to change
between retries.  So we should be able to safely move it to the logic
that sets the initial value of mi->version.

This patch is not supposed to cause a behavioral change.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>

diff --git a/utils/mount/stropts.c b/utils/mount/stropts.c
index c82ddfe2bd9880398b25abc77f9603f881983cfe..c5c4ba157f9ec9d4ff0f5d7e7f644a1b9c226b63 100644 (file)
--- a/utils/mount/stropts.c
+++ b/utils/mount/stropts.c
@@ -303,6 +303,16 @@ static int nfs_set_version(struct nfsmount_info *mi)
        if (strncmp(mi->type, "nfs4", 4) == 0)
                mi->version = 4;
 
+       /*
+        * Before 2.6.32, the kernel NFS client didn't
+        * support "-t nfs vers=4" mounts, so NFS version
+        * 4 cannot be included when autonegotiating
+        * while running on those kernels.
+        */
+       if (mi->version == 0 &&
+           linux_version_code() <= MAKE_VERSION(2, 6, 31))
+               mi->version = 3;
+
        /*
         * If we still don't know, check for version-specific
         * mount options.
@@ -745,6 +755,47 @@ static int nfs_try_mount_v4(struct nfsmount_info *mi)
        return ret;
 }
 
+/*
+ * Handle NFS version and transport protocol
+ * autonegotiation.
+ *
+ * When no version or protocol is specified on the
+ * command line, mount.nfs negotiates with the server
+ * to determine appropriate settings for the new
+ * mount point.
+ *
+ * Returns TRUE if successful, otherwise FALSE.
+ * "errno" is set to reflect the individual error.
+ */
+static int nfs_autonegotiate(struct nfsmount_info *mi)
+{
+       int result;
+
+       result = nfs_try_mount_v4(mi);
+       if (result)
+               return result;
+               
+       switch (errno) {
+       case EPROTONOSUPPORT:
+               /* A clear indication that the server or our
+                * client does not support NFS version 4. */
+               goto fall_back;
+       case ENOENT:
+               /* Legacy Linux servers don't export an NFS
+                * version 4 pseudoroot. */
+               goto fall_back;
+       case EPERM:
+               /* Linux servers prior to 2.6.25 may return
+                * EPERM when NFS version 4 is not supported. */
+               goto fall_back;
+       default:
+               return result;
+       }
+
+fall_back:
+       return nfs_try_mount_v3v2(mi);
+}
+
 /*
  * This is a single pass through the fg/bg loop.
  *
@@ -757,20 +808,8 @@ static int nfs_try_mount(struct nfsmount_info *mi)
 
        switch (mi->version) {
        case 0:
-               if (linux_version_code() > MAKE_VERSION(2, 6, 31)) {
-                       errno = 0;
-                       result = nfs_try_mount_v4(mi);
-                       if (errno != EPROTONOSUPPORT) {
-                               /* 
-                                * To deal with legacy Linux servers that don't
-                                * automatically export a pseudo root, retry
-                                * ENOENT errors using version 3. And for
-                                * Linux servers prior to 2.6.25, retry EPERM
-                                */
-                               if (errno != ENOENT && errno != EPERM)
-                                       break;
-                       }
-               }
+               result = nfs_autonegotiate(mi);
+               break;
        case 2:
        case 3:
                result = nfs_try_mount_v3v2(mi);