Determine the hostid on demand.

Currently, the SPL tries to determine the hostid at module load. The
hostid is usually determined by running the userland program "hostid"
during module initialization.

Unfortunately, when the module initializes, it may be way too soon to be
able to run any userland programs. This is especially true when the
module is compiled directly inside the kernel (built-in); in that case,
the SPL would try to run hostid when the kernel is still initializing,
which of course is doomed to fail.

This patch fixes the issue by deferring hostid generation until
something actually needs the hostid (that is, when zone_get_hostid() is
called), thus switching to a "on-initialization" model to a "on-demand"
(lazy loading) model. ZFS only needs the hostid when some pool
operations are requested, and this always happens way after the kernel
has finished initialization, thus solving the problem.

Signed-off-by: Brian Behlendorf <[email protected]>
Issue openzfs/zfs#851

module/spl/spl-generic.c

@@ -546,11 +546,29 @@ hostid_exec(void)
 uint32_t
 zone_get_hostid(void *zone)
 {
+	static int first = 1;
 	unsigned long hostid;
+	int rc;
 
 	/* Only the global zone is supported */
 	ASSERT(zone == NULL);
 
+	if (first) {
+		first = 0;
+
+		/*
+		 * Get the hostid if it was not passed as a module parameter.
+		 * Try reading the /etc/hostid file directly, and then fall
+		 * back to calling the /usr/bin/hostid utility.
+		 */
+		if ((spl_hostid == HW_INVALID_HOSTID) &&
+		    (rc = hostid_read()) && (rc = hostid_exec()))
+			return HW_INVALID_HOSTID;
+
+		printk(KERN_NOTICE "SPL: using hostid 0x%08x\n",
+			(unsigned int) spl_hostid);
+	}
+
 	if (ddi_strtoul(hw_serial, NULL, HW_HOSTID_LEN-1, &hostid) != 0)
 		return HW_INVALID_HOSTID;
 
@@ -632,16 +650,6 @@ __init spl_init(void)
 	if ((rc = spl_zlib_init()))
 		SGOTO(out9, rc);
 
-	/*
-	 * Get the hostid if it was not passed as a module parameter. Try
-	 * reading the /etc/hostid file directly, and then fall back to calling
-	 * the /usr/bin/hostid utility.
-	 */
-
-	if (spl_hostid == HW_INVALID_HOSTID
-	  && (rc = hostid_read()) && (rc = hostid_exec()))
-		SGOTO(out10, rc = -EADDRNOTAVAIL);
-
 #ifndef HAVE_KALLSYMS_LOOKUP_NAME
 	if ((rc = set_kallsyms_lookup_name()))
 		SGOTO(out10, rc = -EADDRNOTAVAIL);
@@ -653,9 +661,8 @@ __init spl_init(void)
 	if ((rc = spl_vn_init_kallsyms_lookup()))
 		SGOTO(out10, rc);
 
-	printk(KERN_NOTICE "SPL: Loaded module v%s-%s%s, using hostid "
-	       "0x%08x\n", SPL_META_VERSION, SPL_META_RELEASE, SPL_DEBUG_STR,
-	       (unsigned int) spl_hostid);
+	printk(KERN_NOTICE "SPL: Loaded module v%s-%s%s\n", SPL_META_VERSION,
+	       SPL_META_RELEASE, SPL_DEBUG_STR);
 	SRETURN(rc);
 out10:
 	spl_zlib_fini();