From c93d9dff36470434a3677225b820c14986075706 Mon Sep 17 00:00:00 2001
From: Brian Behlendorf <behlendorf1@llnl.gov>
Date: Mon, 10 Jul 2017 15:24:52 -0400
Subject: [PATCH] Don't cache the system hostid

Historically the SPL cached the system hostid the first time it
was accessed.  This was done to speed up subsequent accesses.
But in practice the system host id is rarely accessed and its
inconvenient that it doesn't promptly detect /etc/hostid
configuration changes.  Therefore, zone_get_hostid() has been
updated to always refresh the system hostid reported.

Reviewed-by: Olaf Faaland <faaland1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #626
---
 module/spl/spl-generic.c | 73 +++++++++++++++-------------------------
 module/spl/spl-proc.c    |  3 +-
 2 files changed, 30 insertions(+), 46 deletions(-)

diff --git a/module/spl/spl-generic.c b/module/spl/spl-generic.c
index a9445eb37a9c..10061620e716 100644
--- a/module/spl/spl-generic.c
+++ b/module/spl/spl-generic.c
@@ -499,80 +499,63 @@ module_param(spl_hostid_path, charp, 0444);
 MODULE_PARM_DESC(spl_hostid_path, "The system hostid file (/etc/hostid)");
 
 static int
-hostid_read(void)
+hostid_read(uint32_t *hostid)
 {
-	int result;
 	uint64_t size;
 	struct _buf *file;
-	uint32_t hostid = 0;
+	uint32_t value = 0;
+	int error;
 
 	file = kobj_open_file(spl_hostid_path);
-
 	if (file == (struct _buf *)-1)
-		return -1;
-
-	result = kobj_get_filesize(file, &size);
+		return (ENOENT);
 
-	if (result != 0) {
-		printk(KERN_WARNING
-		       "SPL: kobj_get_filesize returned %i on %s\n",
-		       result, spl_hostid_path);
+	error = kobj_get_filesize(file, &size);
+	if (error) {
 		kobj_close_file(file);
-		return -2;
+		return (error);
 	}
 
 	if (size < sizeof(HW_HOSTID_MASK)) {
-		printk(KERN_WARNING
-		       "SPL: Ignoring the %s file because it is %llu bytes; "
-		       "expecting %lu bytes instead.\n", spl_hostid_path,
-		       size, (unsigned long)sizeof(HW_HOSTID_MASK));
 		kobj_close_file(file);
-		return -3;
+		return (EINVAL);
 	}
 
-	/* Read directly into the variable like eglibc does. */
-	/* Short reads are okay; native behavior is preserved. */
-	result = kobj_read_file(file, (char *)&hostid, sizeof(hostid), 0);
-
-	if (result < 0) {
-		printk(KERN_WARNING
-		       "SPL: kobj_read_file returned %i on %s\n",
-		       result, spl_hostid_path);
+	/*
+	 * Read directly into the variable like eglibc does.
+	 * Short reads are okay; native behavior is preserved.
+	 */
+	error = kobj_read_file(file, (char *)&value, sizeof(value), 0);
+	if (error < 0) {
 		kobj_close_file(file);
-		return -4;
+		return (EIO);
 	}
 
 	/* Mask down to 32 bits like coreutils does. */
-	spl_hostid = hostid & HW_HOSTID_MASK;
+	*hostid = (value & HW_HOSTID_MASK);
 	kobj_close_file(file);
+
 	return 0;
 }
 
+/*
+ * Return the system hostid.  Preferentially use the spl_hostid module option
+ * when set, otherwise use the value in the /etc/hostid file.
+ */
 uint32_t
 zone_get_hostid(void *zone)
 {
-	static int first = 1;
-
-	/* Only the global zone is supported */
-	ASSERT(zone == NULL);
+	uint32_t hostid;
 
-	if (first) {
-		first = 0;
+	ASSERT3P(zone, ==, NULL);
 
-		spl_hostid &= HW_HOSTID_MASK;
-		/*
-		 * Get the hostid if it was not passed as a module parameter.
-		 * Try reading the /etc/hostid file directly.
-		 */
-		if (spl_hostid == 0 && hostid_read())
-			spl_hostid = 0;
+	if (spl_hostid != 0)
+		return ((uint32_t)(spl_hostid & HW_HOSTID_MASK));
 
+	if (hostid_read(&hostid) == 0)
+		return (hostid);
 
-		printk(KERN_NOTICE "SPL: using hostid 0x%08x\n",
-			(unsigned int) spl_hostid);
-	}
-
-	return spl_hostid;
+	return (0);
 }
 EXPORT_SYMBOL(zone_get_hostid);
 
diff --git a/module/spl/spl-proc.c b/module/spl/spl-proc.c
index d6159b4b60fa..bffbcc607579 100644
--- a/module/spl/spl-proc.c
+++ b/module/spl/spl-proc.c
@@ -203,7 +203,8 @@ proc_dohostid(struct ctl_table *table, int write,
                         return (-EINVAL);
 
         } else {
-                len = snprintf(str, sizeof(str), "%lx", spl_hostid);
+                len = snprintf(str, sizeof(str), "%lx",
+		    (unsigned long) zone_get_hostid(NULL));
                 if (*ppos >= len)
                         rc = 0;
                 else