linux/libspl: gethostid: read from /proc/sys/kernel/spl/hostid, simplify

Fixes get_system_hostid() if it was set via the aforementioned sysctl
and simplifies the code a bit.  The kernel and user-space must agree,
after all.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #11879

diff --git a/lib/libspl/os/linux/gethostid.c b/lib/libspl/os/linux/gethostid.c
index 457d5bf6fa3e2c2a6276105ee34d7d265bd0fc9d..c04b7fd3eef3870cb61232e7475b65a9d2e4f23c 100644 (file)
--- a/lib/libspl/os/linux/gethostid.c
+++ b/lib/libspl/os/linux/gethostid.c
@@ -40,47 +40,40 @@ get_spl_hostid(void)
         * Allow the hostid to be subverted for testing.
         */
        env = getenv("ZFS_HOSTID");
-       if (env) {
-               hostid = strtoull(env, NULL, 0);
-               return (hostid & HOSTID_MASK);
-       }
+       if (env)
+               return (strtoull(env, NULL, 0));
 
-       f = fopen("/sys/module/spl/parameters/spl_hostid", "re");
+       f = fopen("/proc/sys/kernel/spl/hostid", "re");
        if (!f)
                return (0);
 
-       if (fscanf(f, "%lu", &hostid) != 1)
+       if (fscanf(f, "%lx", &hostid) != 1)
                hostid = 0;
 
        fclose(f);
 
-       return (hostid & HOSTID_MASK);
+       return (hostid);
 }
 
 unsigned long
 get_system_hostid(void)
 {
-       unsigned long system_hostid = get_spl_hostid();
+       unsigned long hostid = get_spl_hostid();
+
        /*
-        * We do not use the library call gethostid() because
-        * it generates a hostid value that the kernel is
-        * unaware of, if the spl_hostid module parameter has not
-        * been set and there is no system hostid file (e.g.
-        * /etc/hostid).  The kernel and userspace must agree.
+        * We do not use gethostid(3) because it can return a bogus ID,
+        * depending on the libc and /etc/hostid presence,
+        * and the kernel and userspace must agree.
         * See comments above hostid_read() in the SPL.
         */
-       if (system_hostid == 0) {
-               int fd, rc;
-               unsigned long hostid;
-               int hostid_size = 4;  /* 4 bytes regardless of arch */
-
-               fd = open("/etc/hostid", O_RDONLY | O_CLOEXEC);
+       if (hostid == 0) {
+               int fd = open("/etc/hostid", O_RDONLY | O_CLOEXEC);
                if (fd >= 0) {
-                       rc = read(fd, &hostid, hostid_size);
-                       if (rc > 0)
-                               system_hostid = (hostid & HOSTID_MASK);
-                       close(fd);
+                       if (read(fd, &hostid, 4) < 0)
+                               hostid = 0;
+                       (void) close(fd);
                }
        }
-       return (system_hostid);
+
+       return (hostid & HOSTID_MASK);
 }