From 34ae0ae1749f297c23c3c1680ea552df94ae2122 Mon Sep 17 00:00:00 2001 From: Olaf Faaland Date: Thu, 25 May 2017 13:32:06 -0700 Subject: [PATCH] Make hostid consistent in user and kernel space If no spl_hostid was set, and no /etc/hostid file existed, the user and kernel would have different values for the hostid. The kernel's would be 0. User space's would depend on the libc implementation. On systems with glibc, it would be a generated value, probably the first 4 bytes of an IP address (see man 3 gethostid and comments above hostid_read in SPL for details). This then causes the hostid stored in the labels and in the pool config not to match the hostid userspace obtains from get_system_hostid(). Since the kernel has no way to know the libc's generated hostid value, it serves no purpose for ZFS to use the value. This patch changes user space's get_system_hostid() to conform to the kernel's method, first checking for the spl_hostid via sysfs, and then reading from /etc/hostid directly. It does not look up spl_hostid_path, because if that is set and the file it pointed to exists, spl_hostid will reflect its contents. It eliminates the call to libc's gethostid(). Reviewed by: Matthew Ahrens Reviewed-by: Giuseppe Di Natale Reviewed-by: Ned Bass Reviewed-by: Andreas Dilger Reviewed-by: Brian Behlendorf Signed-off-by: Olaf Faaland Closes #745 Closes #6279 --- lib/libzpool/kernel.c | 40 +++++++++++++++++++++++++++++++++++++--- 1 file changed, 37 insertions(+), 3 deletions(-) diff --git a/lib/libzpool/kernel.c b/lib/libzpool/kernel.c index ed9c1a9ef7..e67d13c926 100644 --- a/lib/libzpool/kernel.c +++ b/lib/libzpool/kernel.c @@ -1288,27 +1288,61 @@ umem_out_of_memory(void) return (0); } +#define HOSTID_MASK 0xffffffff + static unsigned long get_spl_hostid(void) { FILE *f; unsigned long hostid; + char *env; + + /* + * Allow the hostid to be subverted for testing. + */ + env = getenv("ZFS_HOSTID"); + if (env) { + hostid = strtoull(env, NULL, 0); + return (hostid & HOSTID_MASK); + } f = fopen("/sys/module/spl/parameters/spl_hostid", "r"); if (!f) return (0); + if (fscanf(f, "%lu", &hostid) != 1) hostid = 0; + fclose(f); - return (hostid & 0xffffffff); + + return (hostid & HOSTID_MASK); } unsigned long get_system_hostid(void) { unsigned long system_hostid = get_spl_hostid(); - if (system_hostid == 0) - system_hostid = gethostid() & 0xffffffff; + /* + * 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. + * 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); + if (fd >= 0) { + rc = read(fd, &hostid, hostid_size); + if (rc > 0) + system_hostid = (hostid & HOSTID_MASK); + close(fd); + } + } return (system_hostid); }