]> git.decadent.org.uk Git - nfs-utils.git/blobdiff - utils/mount/stropts.c
mount.nfs: Don't do anything fancy if this is a remount
[nfs-utils.git] / utils / mount / stropts.c
index c369136c702b93ae0c0937721943d54118cd9d1c..50a1a2a06626a72ba2c09fe656df3331e66a85b1 100644 (file)
 #include <netinet/in.h>
 #include <arpa/inet.h>
 
+#include "sockaddr.h"
 #include "xcommon.h"
 #include "mount.h"
 #include "nls.h"
+#include "nfsrpc.h"
 #include "mount_constants.h"
 #include "stropts.h"
 #include "error.h"
 #include "parse_opt.h"
 #include "version.h"
 #include "parse_dev.h"
+#include "conffile.h"
+
+#ifndef HAVE_DECL_AI_ADDRCONFIG
+#define AI_ADDRCONFIG  0
+#endif
 
 #ifndef NFS_PROGRAM
 #define NFS_PROGRAM    (100003)
@@ -80,17 +87,36 @@ struct nfsmount_info {
                                *node,          /* mounted-on dir */
                                *type;          /* "nfs" or "nfs4" */
        char                    *hostname;      /* server's hostname */
+       struct addrinfo         *address;       /* server's addresses */
 
        struct mount_options    *options;       /* parsed mount options */
        char                    **extra_opts;   /* string for /etc/mtab */
 
+       unsigned long           version;        /* NFS version */
        int                     flags,          /* MS_ flags */
                                fake,           /* actually do the mount? */
                                child;          /* forked bg child? */
-
-       sa_family_t             family;         /* supported address family */
 };
 
+#ifdef MOUNT_CONFIG
+static void nfs_default_version(struct nfsmount_info *mi);
+
+static void nfs_default_version(struct nfsmount_info *mi)
+{
+       extern unsigned long config_default_vers;
+       /*
+        * Use the default value set in the config file when
+        * the version has not been explicitly set.
+        */
+       if (mi->version == 0 && config_default_vers) {
+               if (config_default_vers < 4)
+                       mi->version = config_default_vers;
+       }
+}
+#else
+inline void nfs_default_version(struct nfsmount_info *mi) {}
+#endif /* MOUNT_CONFIG */
+
 /*
  * Obtain a retry timeout value based on the value of the "retry=" option.
  *
@@ -132,12 +158,14 @@ static int nfs_append_generic_address_option(const struct sockaddr *sap,
 {
        char address[NI_MAXHOST];
        char new_option[512];
+       int len;
 
        if (!nfs_present_sockaddr(sap, salen, address, sizeof(address)))
                goto out_err;
 
-       if (snprintf(new_option, sizeof(new_option), "%s=%s",
-                                       keyword, address) >= sizeof(new_option))
+       len = snprintf(new_option, sizeof(new_option), "%s=%s",
+                                               keyword, address);
+       if (len < 0 || (size_t)len >= sizeof(new_option))
                goto out_err;
 
        if (po_append(options, new_option) != PO_SUCCEEDED)
@@ -181,9 +209,9 @@ static int nfs_append_clientaddr_option(const struct sockaddr *sap,
                                        socklen_t salen,
                                        struct mount_options *options)
 {
-       struct sockaddr_storage dummy;
-       struct sockaddr *my_addr = (struct sockaddr *)&dummy;
-       socklen_t my_len = sizeof(dummy);
+       union nfs_sockaddr address;
+       struct sockaddr *my_addr = &address.sa;
+       socklen_t my_len = sizeof(address);
 
        if (po_contains(options, "clientaddr") == PO_FOUND)
                return 1;
@@ -195,22 +223,33 @@ static int nfs_append_clientaddr_option(const struct sockaddr *sap,
 }
 
 /*
- * Resolve the 'mounthost=' hostname and append a new option using
- * the resulting address.
+ * Determine whether to append a 'mountaddr=' option.  The option is needed if:
+ *
+ *   1. "mounthost=" was specified, or
+ *   2. The address families for proto= and mountproto= are different.
  */
-static int nfs_fix_mounthost_option(const sa_family_t family,
-                                   struct mount_options *options)
+static int nfs_fix_mounthost_option(struct mount_options *options,
+               const char *nfs_hostname)
 {
-       struct sockaddr_storage dummy;
-       struct sockaddr *sap = (struct sockaddr *)&dummy;
-       socklen_t salen = sizeof(dummy);
+       union nfs_sockaddr address;
+       struct sockaddr *sap = &address.sa;
+       socklen_t salen = sizeof(address);
+       sa_family_t nfs_family, mnt_family;
        char *mounthost;
 
+       if (!nfs_nfs_proto_family(options, &nfs_family))
+               return 0;
+       if (!nfs_mount_proto_family(options, &mnt_family))
+               return 0;
+
        mounthost = po_get(options, "mounthost");
-       if (!mounthost)
-               return 1;
+       if (mounthost == NULL) {
+               if (nfs_family == mnt_family)
+                       return 1;
+               mounthost = (char *)nfs_hostname;
+       }
 
-       if (!nfs_name_to_address(mounthost, family, sap, &salen)) {
+       if (!nfs_lookup(mounthost, mnt_family, sap, &salen)) {
                nfs_error(_("%s: unable to determine mount server's address"),
                                progname);
                return 0;
@@ -256,57 +295,85 @@ static int nfs_append_sloppy_option(struct mount_options *options)
        return 1;
 }
 
+static int nfs_set_version(struct nfsmount_info *mi)
+{
+       if (!nfs_nfs_version(mi->options, &mi->version))
+               return 0;
+
+       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.
+        */
+       if (mi->version == 0) {
+               if (po_contains(mi->options, "mounthost") ||
+                   po_contains(mi->options, "mountaddr") ||
+                   po_contains(mi->options, "mountvers") ||
+                   po_contains(mi->options, "mountproto"))
+                       mi->version = 3;
+       }
+
+       /*
+        * If enabled, see if the default version was
+        * set in the config file
+        */
+       nfs_default_version(mi);
+       
+       return 1;
+}
+
 /*
- * Set up mandatory NFS mount options.
+ * Set up mandatory non-version specific NFS mount options.
  *
  * Returns 1 if successful; otherwise zero.
  */
 static int nfs_validate_options(struct nfsmount_info *mi)
 {
-       struct sockaddr_storage dummy;
-       struct sockaddr *sap = (struct sockaddr *)&dummy;
-       socklen_t salen = sizeof(dummy);
+       struct addrinfo hint = {
+               .ai_protocol    = (int)IPPROTO_UDP,
+               .ai_flags       = AI_ADDRCONFIG,
+       };
+       sa_family_t family;
+       int error;
 
        if (!nfs_parse_devname(mi->spec, &mi->hostname, NULL))
                return 0;
 
-       if (!nfs_name_to_address(mi->hostname, mi->family, sap, &salen))
+       if (!nfs_nfs_proto_family(mi->options, &family))
                return 0;
 
-       if (strncmp(mi->type, "nfs4", 4) == 0) {
-               if (!nfs_append_clientaddr_option(sap, salen, mi->options))
-                       return 0;
-       } else {
-               if (!nfs_fix_mounthost_option(mi->family, mi->options))
-                       return 0;
-               if (!mi->fake && !nfs_verify_lock_option(mi->options))
-                       return 0;
+       hint.ai_family = (int)family;
+       error = getaddrinfo(mi->hostname, NULL, &hint, &mi->address);
+       if (error != 0) {
+               nfs_error(_("%s: Failed to resolve server %s: %s"),
+                       progname, mi->hostname, gai_strerror(error));
+               mi->address = NULL;
+               return 0;
        }
 
+       if (!nfs_set_version(mi))
+               return 0;
+
        if (!nfs_append_sloppy_option(mi->options))
                return 0;
 
-       return nfs_append_addr_option(sap, salen, mi->options);
-}
+       if (!nfs_append_addr_option(mi->address->ai_addr,
+                                       mi->address->ai_addrlen, mi->options))
+               return 0;
 
-/*
- * Distinguish between permanent and temporary errors.
- *
- * Returns 0 if the passed-in error is temporary, thus the
- * mount system call should be retried; returns one if the
- * passed-in error is permanent, thus the mount system call
- * should not be retried.
- */
-static int nfs_is_permanent_error(int error)
-{
-       switch (error) {
-       case ESTALE:
-       case ETIMEDOUT:
-       case ECONNREFUSED:
-               return 0;       /* temporary */
-       default:
-               return 1;       /* permanent */
-       }
+       return 1;
 }
 
 /*
@@ -326,26 +393,27 @@ static int nfs_extract_server_addresses(struct mount_options *options,
        option = po_get(options, "addr");
        if (option == NULL)
                return 0;
-       if (!nfs_string_to_sockaddr(option, strlen(option),
-                                               nfs_saddr, nfs_salen))
+       if (!nfs_string_to_sockaddr(option, nfs_saddr, nfs_salen))
                return 0;
 
        option = po_get(options, "mountaddr");
        if (option == NULL) {
                memcpy(mnt_saddr, nfs_saddr, *nfs_salen);
                *mnt_salen = *nfs_salen;
-       } else if (!nfs_string_to_sockaddr(option, strlen(option),
-                                               mnt_saddr, mnt_salen))
+       } else if (!nfs_string_to_sockaddr(option, mnt_saddr, mnt_salen))
                return 0;
 
        return 1;
 }
 
 static int nfs_construct_new_options(struct mount_options *options,
+                                    struct sockaddr *nfs_saddr,
                                     struct pmap *nfs_pmap,
+                                    struct sockaddr *mnt_saddr,
                                     struct pmap *mnt_pmap)
 {
        char new_option[64];
+       char *netid;
 
        po_remove_all(options, "nfsprog");
        po_remove_all(options, "mountprog");
@@ -362,20 +430,14 @@ static int nfs_construct_new_options(struct mount_options *options,
        po_remove_all(options, "proto");
        po_remove_all(options, "udp");
        po_remove_all(options, "tcp");
-       switch (nfs_pmap->pm_prot) {
-       case IPPROTO_TCP:
-               snprintf(new_option, sizeof(new_option) - 1,
-                        "proto=tcp");
-               if (po_append(options, new_option) == PO_FAILED)
-                       return 0;
-               break;
-       case IPPROTO_UDP:
-               snprintf(new_option, sizeof(new_option) - 1,
-                        "proto=udp");
-               if (po_append(options, new_option) == PO_FAILED)
-                       return 0;
-               break;
-       }
+       netid = nfs_get_netid(nfs_saddr->sa_family, nfs_pmap->pm_prot);
+       if (netid == NULL)
+               return 0;
+       snprintf(new_option, sizeof(new_option) - 1,
+                        "proto=%s", netid);
+       free(netid);
+       if (po_append(options, new_option) == PO_FAILED)
+               return 0;
 
        po_remove_all(options, "port");
        if (nfs_pmap->pm_port != NFS_PORT) {
@@ -392,20 +454,14 @@ static int nfs_construct_new_options(struct mount_options *options,
                return 0;
 
        po_remove_all(options, "mountproto");
-       switch (mnt_pmap->pm_prot) {
-       case IPPROTO_TCP:
-               snprintf(new_option, sizeof(new_option) - 1,
-                        "mountproto=tcp");
-               if (po_append(options, new_option) == PO_FAILED)
-                       return 0;
-               break;
-       case IPPROTO_UDP:
-               snprintf(new_option, sizeof(new_option) - 1,
-                        "mountproto=udp");
-               if (po_append(options, new_option) == PO_FAILED)
-                       return 0;
-               break;
-       }
+       netid = nfs_get_netid(mnt_saddr->sa_family, mnt_pmap->pm_prot);
+       if (netid == NULL)
+               return 0;
+       snprintf(new_option, sizeof(new_option) - 1,
+                        "mountproto=%s", netid);
+       free(netid);
+       if (po_append(options, new_option) == PO_FAILED)
+               return 0;
 
        po_remove_all(options, "mountport");
        snprintf(new_option, sizeof(new_option) - 1,
@@ -423,76 +479,107 @@ static int nfs_construct_new_options(struct mount_options *options,
  *
  * To handle version and transport protocol fallback properly, we
  * need to parse some of the mount options in order to set up a
- * portmap probe.  Mount options that nfs_rewrite_mount_options()
+ * portmap probe.  Mount options that nfs_rewrite_pmap_mount_options()
  * doesn't recognize are left alone.
  *
- * Returns a new group of mount options if successful; otherwise
- * NULL is returned if some failure occurred.
+ * Returns TRUE if rewriting was successful; otherwise
+ * FALSE is returned if some failure occurred.
  */
-static struct mount_options *nfs_rewrite_mount_options(char *str)
+static int
+nfs_rewrite_pmap_mount_options(struct mount_options *options)
 {
-       struct mount_options *options;
-       struct sockaddr_storage nfs_address;
-       struct sockaddr *nfs_saddr = (struct sockaddr *)&nfs_address;
-       socklen_t nfs_salen;
+       union nfs_sockaddr nfs_address;
+       struct sockaddr *nfs_saddr = &nfs_address.sa;
+       socklen_t nfs_salen = sizeof(nfs_address);
        struct pmap nfs_pmap;
-       struct sockaddr_storage mnt_address;
-       struct sockaddr *mnt_saddr = (struct sockaddr *)&mnt_address;
-       socklen_t mnt_salen;
+       union nfs_sockaddr mnt_address;
+       struct sockaddr *mnt_saddr = &mnt_address.sa;
+       socklen_t mnt_salen = sizeof(mnt_address);
+       unsigned long protocol;
        struct pmap mnt_pmap;
 
-       options = po_split(str);
-       if (!options) {
-               errno = EFAULT;
-               return NULL;
+       /*
+        * Version and transport negotiation is not required
+        * and does not work for RDMA mounts.
+        */
+       if (!nfs_nfs_protocol(options, &protocol)) {
+               errno = EINVAL;
+               return 0;
        }
+       if (protocol == NFSPROTO_RDMA)
+               goto out;
 
+       /*
+        * Extract just the options needed to contact server.
+        * Bail now if any of these have bad values.
+        */
        if (!nfs_extract_server_addresses(options, nfs_saddr, &nfs_salen,
                                                mnt_saddr, &mnt_salen)) {
                errno = EINVAL;
-               goto err;
+               return 0;
+       }
+       if (!nfs_options2pmap(options, &nfs_pmap, &mnt_pmap)) {
+               errno = EINVAL;
+               return 0;
        }
 
-       nfs_options2pmap(options, &nfs_pmap, &mnt_pmap);
-
-       /* The kernel NFS client doesn't support changing the RPC program
-        * number for these services, so reset these fields before probing
-        * the server's ports.  */
+       /*
+        * The kernel NFS client doesn't support changing the RPC
+        * program number for these services, so force the value of
+        * these fields before probing the server's ports.
+        */
        nfs_pmap.pm_prog = NFS_PROGRAM;
        mnt_pmap.pm_prog = MOUNTPROG;
 
+       /*
+        * If the server's rpcbind service isn't available, we can't
+        * negotiate.  Bail now if we can't contact it.
+        */
        if (!nfs_probe_bothports(mnt_saddr, mnt_salen, &mnt_pmap,
                                 nfs_saddr, nfs_salen, &nfs_pmap)) {
                errno = ESPIPE;
-               goto err;
+               if (rpc_createerr.cf_stat == RPC_PROGNOTREGISTERED)
+                       errno = EOPNOTSUPP;
+               else if (rpc_createerr.cf_error.re_errno != 0)
+                       errno = rpc_createerr.cf_error.re_errno;
+               return 0;
        }
 
-       if (!nfs_construct_new_options(options, &nfs_pmap, &mnt_pmap)) {
-               errno = EINVAL;
-               goto err;
+       if (!nfs_construct_new_options(options, nfs_saddr, &nfs_pmap,
+                                       mnt_saddr, &mnt_pmap)) {
+               if (rpc_createerr.cf_stat == RPC_UNKNOWNPROTO)
+                       errno = EPROTONOSUPPORT;
+               else
+                       errno = EINVAL;
+               return 0;
        }
 
+out:
        errno = 0;
-       return options;
-
-err:
-       po_destroy(options);
-       return NULL;
+       return 1;
 }
 
 /*
  * Do the mount(2) system call.
  *
- * Returns 1 if successful, otherwise zero.
+ * Returns TRUE if successful, otherwise FALSE.
  * "errno" is set to reflect the individual error.
  */
-static int nfs_sys_mount(const struct nfsmount_info *mi, const char *type,
-                        const char *options)
+static int nfs_sys_mount(struct nfsmount_info *mi, struct mount_options *opts)
 {
+       char *options = NULL;
        int result;
 
-       result = mount(mi->spec, mi->node, type,
-                               mi->flags & ~(MS_USER|MS_USERS), options);
+       if (po_join(opts, &options) == PO_FAILED) {
+               errno = EIO;
+               return 0;
+       }
+
+       if (mi->fake)
+               return 1;
+
+       result = mount(mi->spec, mi->node, mi->type,
+                       mi->flags & ~(MS_USER|MS_USERS), options);
        if (verbose && result) {
                int save = errno;
                nfs_error(_("%s: mount(2): %s"), progname, strerror(save));
@@ -501,128 +588,266 @@ static int nfs_sys_mount(const struct nfsmount_info *mi, const char *type,
        return !result;
 }
 
-/*
- * Retry an NFS mount that failed because the requested service isn't
- * available on the server.
- *
- * Returns 1 if successful.  Otherwise, returns zero.
- * "errno" is set to reflect the individual error.
- *
- * Side effect: If the retry is successful, both 'options' and
- * 'extra_opts' are updated to reflect the mount options that worked.
- * If the retry fails, 'options' and 'extra_opts' are left unchanged.
- */
-static int nfs_retry_nfs23mount(struct nfsmount_info *mi)
+static int nfs_do_mount_v3v2(struct nfsmount_info *mi,
+               struct sockaddr *sap, socklen_t salen)
 {
-       struct mount_options *retry_options;
-       char *retry_str = NULL;
-       char **extra_opts = mi->extra_opts;
+       struct mount_options *options = po_dup(mi->options);
+       int result = 0;
 
-       retry_options = nfs_rewrite_mount_options(*extra_opts);
-       if (!retry_options)
-               return 0;
+       if (!options) {
+               errno = ENOMEM;
+               return result;
+       }
+       errno = 0;
+       if (!nfs_append_addr_option(sap, salen, options)) {
+               if (errno == 0)
+                       errno = EINVAL;
+               goto out_fail;
+       }
 
-       if (po_join(retry_options, &retry_str) == PO_FAILED) {
-               po_destroy(retry_options);
-               errno = EIO;
-               return 0;
+       if (!nfs_fix_mounthost_option(options, mi->hostname)) {
+               if (errno == 0)
+                       errno = EINVAL;
+               goto out_fail;
+       }
+       if (!mi->fake && !nfs_verify_lock_option(options)) {
+               if (errno == 0)
+                       errno = EINVAL;
+               goto out_fail;
+       }
+
+       /*
+        * Options we negotiate below may be stale by the time this
+        * file system is unmounted.  In order to force umount.nfs
+        * to renegotiate with the server, only write the user-
+        * specified options, and not negotiated options, to /etc/mtab.
+        */
+       if (po_join(options, mi->extra_opts) == PO_FAILED) {
+               errno = ENOMEM;
+               goto out_fail;
        }
 
        if (verbose)
-               printf(_("%s: text-based options (retry): '%s'\n"),
-                       progname, retry_str);
+               printf(_("%s: trying text-based options '%s'\n"),
+                       progname, *mi->extra_opts);
 
-       if (!nfs_sys_mount(mi, "nfs", retry_str)) {
-               po_destroy(retry_options);
-               free(retry_str);
-               return 0;
-       }
+       if (!nfs_rewrite_pmap_mount_options(options))
+               goto out_fail;
 
-       free(*extra_opts);
-       *extra_opts = retry_str;
-       po_replace(mi->options, retry_options);
-       return 1;
+       result = nfs_sys_mount(mi, options);
+
+out_fail:
+       po_destroy(options);
+       return result;
 }
 
 /*
- * Attempt an NFSv2/3 mount via a mount(2) system call.  If the kernel
- * claims the requested service isn't supported on the server, probe
- * the server to see what's supported, rewrite the mount options,
- * and retry the request.
+ * Attempt a "-t nfs vers=2" or "-t nfs vers=3" mount.
  *
- * Returns 1 if successful.  Otherwise, returns zero.
+ * Returns TRUE if successful, otherwise FALSE.
  * "errno" is set to reflect the individual error.
- *
- * Side effect: If the retry is successful, both 'options' and
- * 'extra_opts' are updated to reflect the mount options that worked.
- * If the retry fails, 'options' and 'extra_opts' are left unchanged.
  */
-static int nfs_try_nfs23mount(struct nfsmount_info *mi)
+static int nfs_try_mount_v3v2(struct nfsmount_info *mi)
 {
-       char **extra_opts = mi->extra_opts;
+       struct addrinfo *ai;
+       int ret;
+
+       for (ai = mi->address; ai != NULL; ai = ai->ai_next) {
+               ret = nfs_do_mount_v3v2(mi, ai->ai_addr, ai->ai_addrlen);
+               if (ret != 0)
+                       return ret;
+
+               switch (errno) {
+               case ECONNREFUSED:
+               case EOPNOTSUPP:
+               case EHOSTUNREACH:
+                       continue;
+               default:
+                       break;
+               }
+       }
+       return ret;
+}
 
-       if (po_join(mi->options, extra_opts) == PO_FAILED) {
-               errno = EIO;
-               return 0;
+static int nfs_do_mount_v4(struct nfsmount_info *mi,
+               struct sockaddr *sap, socklen_t salen)
+{
+       struct mount_options *options = po_dup(mi->options);
+       int result = 0;
+
+       if (!options) {
+               errno = ENOMEM;
+               return result;
        }
 
-       if (verbose)
-               printf(_("%s: text-based options: '%s'\n"),
-                       progname, *extra_opts);
+       if (mi->version == 0) {
+               if (po_contains(options, "mounthost") ||
+                       po_contains(options, "mountaddr") ||
+                       po_contains(options, "mountvers") ||
+                       po_contains(options, "mountproto")) {
+               /*
+                * Since these mountd options are set assume version 3
+                * is wanted so error out with EPROTONOSUPPORT so the
+                * protocol negation starts with v3.
+                */
+                       errno = EPROTONOSUPPORT;
+                       goto out_fail;
+               }
+               if (po_append(options, "vers=4") == PO_FAILED) {
+                       errno = EINVAL;
+                       goto out_fail;
+               }
+       }
 
-       if (mi->fake)
-               return 1;
+       if (!nfs_append_addr_option(sap, salen, options)) {
+               errno = EINVAL;
+               goto out_fail;
+       }
 
-       if (nfs_sys_mount(mi, "nfs", *extra_opts))
-               return 1;
+       if (!nfs_append_clientaddr_option(sap, salen, options)) {
+               errno = EINVAL;
+               goto out_fail;
+       }
 
        /*
-        * The kernel returns EOPNOTSUPP if the RPC bind failed,
-        * and EPROTONOSUPPORT if the version isn't supported.
+        * Update option string to be recorded in /etc/mtab.
         */
-       if (errno != EOPNOTSUPP && errno != EPROTONOSUPPORT)
-               return 0;
+       if (po_join(options, mi->extra_opts) == PO_FAILED) {
+               errno = ENOMEM;
+               goto out_fail;
+       }
 
-       return nfs_retry_nfs23mount(mi);
+       if (verbose)
+               printf(_("%s: trying text-based options '%s'\n"),
+                       progname, *mi->extra_opts);
+
+       result = nfs_sys_mount(mi, options);
+
+out_fail:
+       po_destroy(options);
+       return result;
 }
 
 /*
- * Attempt an NFS v4 mount via a mount(2) system call.
+ * Attempt a "-t nfs -o vers=4" or "-t nfs4" mount.
  *
- * Returns 1 if successful.  Otherwise, returns zero.
+ * Returns TRUE if successful, otherwise FALSE.
  * "errno" is set to reflect the individual error.
  */
-static int nfs_try_nfs4mount(struct nfsmount_info *mi)
+static int nfs_try_mount_v4(struct nfsmount_info *mi)
 {
-       char **extra_opts = mi->extra_opts;
-
-       if (po_join(mi->options, extra_opts) == PO_FAILED) {
-               errno = EIO;
-               return 0;
+       struct addrinfo *ai;
+       int ret;
+
+       for (ai = mi->address; ai != NULL; ai = ai->ai_next) {
+               ret = nfs_do_mount_v4(mi, ai->ai_addr, ai->ai_addrlen);
+               if (ret != 0)
+                       return ret;
+
+               switch (errno) {
+               case ECONNREFUSED:
+               case EHOSTUNREACH:
+                       continue;
+               default:
+                       break;
+               }
        }
+       return ret;
+}
 
-       if (verbose)
-               printf(_("%s: text-based options: '%s'\n"),
-                       progname, *extra_opts);
+/*
+ * 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;
 
-       if (mi->fake)
-               return 1;
+       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;
+       }
 
-       return nfs_sys_mount(mi, "nfs4", *extra_opts);
+fall_back:
+       return nfs_try_mount_v3v2(mi);
 }
 
 /*
- * Perform either an NFSv2/3 mount, or an NFSv4 mount system call.
+ * This is a single pass through the fg/bg loop.
  *
- * Returns 1 if successful.  Otherwise, returns zero.
+ * Returns TRUE if successful, otherwise FALSE.
  * "errno" is set to reflect the individual error.
  */
 static int nfs_try_mount(struct nfsmount_info *mi)
 {
-       if (strncmp(mi->type, "nfs4", 4) == 0)
-               return nfs_try_nfs4mount(mi);
-       else
-               return nfs_try_nfs23mount(mi);
+       int result = 0;
+
+       switch (mi->version) {
+       case 0:
+               result = nfs_autonegotiate(mi);
+               break;
+       case 2:
+       case 3:
+               result = nfs_try_mount_v3v2(mi);
+               break;
+       case 4:
+               result = nfs_try_mount_v4(mi);
+               break;
+       default:
+               errno = EIO;
+       }
+
+       return result;
+}
+
+/*
+ * Distinguish between permanent and temporary errors.
+ *
+ * Basically, we retry if communication with the server has
+ * failed so far, but fail immediately if there is a local
+ * error (like a bad mount option).
+ *
+ * ESTALE is also a temporary error because some servers
+ * return ESTALE when a share is temporarily offline.
+ *
+ * Returns 1 if we should fail immediately, or 0 if we
+ * should retry.
+ */
+static int nfs_is_permanent_error(int error)
+{
+       switch (error) {
+       case ESTALE:
+       case ETIMEDOUT:
+       case ECONNREFUSED:
+       case EHOSTUNREACH:
+               return 0;       /* temporary */
+       default:
+               return 1;       /* permanent */
+       }
 }
 
 /*
@@ -741,6 +966,26 @@ static int nfsmount_bg(struct nfsmount_info *mi)
                return nfsmount_child(mi);
 }
 
+/*
+ * Usually all that is needed for an NFS remount is to change
+ * generic mount options like "sync" or "ro".  These generic
+ * options are controlled by mi->flags, not by text-based
+ * options, and no contact with the server is needed.
+ *
+ * Take care with the /etc/mtab entry for this mount; just
+ * calling update_mtab() will change an "-t nfs -o vers=4"
+ * mount to an "-t nfs -o remount" mount, and that will
+ * confuse umount.nfs.
+ *
+ * Returns a valid mount command exit code.
+ */
+static int nfs_remount(struct nfsmount_info *mi)
+{
+       if (nfs_sys_mount(mi, mi->options))
+               return EX_SUCCESS;
+       return EX_FAIL;
+}
+
 /*
  * Process mount options and try a mount system call.
  *
@@ -757,6 +1002,12 @@ static int nfsmount_start(struct nfsmount_info *mi)
        if (!nfs_validate_options(mi))
                return EX_FAIL;
 
+       /*
+        * Avoid retry and negotiation logic when remounting
+        */
+       if (mi->flags & MS_REMOUNT)
+               return nfs_remount(mi);
+
        if (po_rightmost(mi->options, nfs_background_opttbl) == 0)
                return nfsmount_bg(mi);
        else
@@ -773,6 +1024,8 @@ static int nfsmount_start(struct nfsmount_info *mi)
  *             (input and output argument)
  * @fake: flag indicating whether to carry out the whole operation
  * @child: one if this is a mount daemon (bg)
+ *
+ * Returns a valid mount command exit code.
  */
 int nfsmount_string(const char *spec, const char *node, const char *type,
                    int flags, char **extra_opts, int fake, int child)
@@ -780,16 +1033,12 @@ int nfsmount_string(const char *spec, const char *node, const char *type,
        struct nfsmount_info mi = {
                .spec           = spec,
                .node           = node,
+               .address        = NULL,
                .type           = type,
                .extra_opts     = extra_opts,
                .flags          = flags,
                .fake           = fake,
                .child          = child,
-#ifdef IPV6_SUPPORTED
-               .family         = AF_UNSPEC,    /* either IPv4 or v6 */
-#else
-               .family         = AF_INET,      /* only IPv4 */
-#endif
        };
        int retval = EX_FAIL;
 
@@ -800,6 +1049,7 @@ int nfsmount_string(const char *spec, const char *node, const char *type,
        } else
                nfs_error(_("%s: internal option parsing error"), progname);
 
+       freeaddrinfo(mi.address);
        free(mi.hostname);
        return retval;
 }