From 60b27ebb2532d5607f3b0ec7c4a3c4047a14db44 Mon Sep 17 00:00:00 2001 From: Eric van Gyzen Date: Wed, 14 Oct 2015 14:26:44 +0000 Subject: [PATCH] resolver: automatically reload /etc/resolv.conf On each resolver query, use stat(2) to see if the modification time of /etc/resolv.conf has changed. If so, reload the file and reinitialize the resolver library. However, only call stat(2) if at least two seconds have passed since the last call to stat(2), since calling it on every query could kill performance. This new behavior is enabled by default. Add a "reload-period" option to disable it or change the period of the test. Document this behavior and option in resolv.conf(5). Polish the man page just enough to appease igor. https://lists.freebsd.org/pipermail/freebsd-arch/2015-October/017342.html Reviewed by: kp, wblock Discussed with: jilles, imp, alfred MFC after: 1 month Relnotes: yes Sponsored by: Dell Inc. Differential Revision: https://reviews.freebsd.org/D3867 --- include/resolv.h | 5 ++++- lib/libc/resolv/res_init.c | 22 ++++++++++++++++++++++ lib/libc/resolv/res_state.c | 31 +++++++++++++++++++++++++++++-- share/man/man5/resolver.5 | 18 +++++++++++++++--- 4 files changed, 70 insertions(+), 6 deletions(-) diff --git a/include/resolv.h b/include/resolv.h index e3d4fd12a097..78da3748a20e 100644 --- a/include/resolv.h +++ b/include/resolv.h @@ -176,7 +176,8 @@ struct __res_state { int res_h_errno; /*%< last one set for this context */ int _vcsock; /*%< PRIVATE: for res_send VC i/o */ u_int _flags; /*%< PRIVATE: see below */ - u_int _pad; /*%< make _u 64 bit aligned */ + u_short reload_period; /*%< seconds between stat(resolv.conf)*/ + u_short _pad; /*%< make _u 64 bit aligned */ union { /* On an 32-bit arch this means 512b total. */ char pad[72 - 4*sizeof (int) - 3*sizeof (void *)]; @@ -188,6 +189,8 @@ struct __res_state { } _ext; } _u; u_char *_rnd; /*%< PRIVATE: random state */ + struct timespec conf_mtim; /*%< mod time of loaded resolv.conf */ + time_t conf_stat; /*%< time of last stat(resolv.conf) */ }; typedef struct __res_state *res_state; diff --git a/lib/libc/resolv/res_init.c b/lib/libc/resolv/res_init.c index 4dbd6d1caca2..087e6a862568 100644 --- a/lib/libc/resolv/res_init.c +++ b/lib/libc/resolv/res_init.c @@ -78,6 +78,7 @@ __FBSDID("$FreeBSD$"); #include #include #include +#include #include #include @@ -227,6 +228,7 @@ __res_vinit(res_state statp, int preinit) { statp->pfcode = 0; statp->_vcsock = -1; statp->_flags = 0; + statp->reload_period = 2; statp->qhook = NULL; statp->rhook = NULL; statp->_u._ext.nscount = 0; @@ -321,6 +323,22 @@ __res_vinit(res_state statp, int preinit) { nserv = 0; if ((fp = fopen(_PATH_RESCONF, "re")) != NULL) { + struct stat sb; + struct timespec now; + + if (_fstat(fileno(fp), &sb) == 0) { + statp->conf_mtim = sb.st_mtim; + if (clock_gettime(CLOCK_MONOTONIC_FAST, &now) == 0) { + statp->conf_stat = now.tv_sec; + } else { + statp->conf_stat = 0; + } + } else { + statp->conf_mtim.tv_sec = 0; + statp->conf_mtim.tv_nsec = 0; + statp->conf_stat = 0; + } + /* read the config file */ while (fgets(buf, sizeof(buf), fp) != NULL) { /* skip comments */ @@ -666,6 +684,10 @@ res_setoptions(res_state statp, const char *options, const char *source) } else if (!strncmp(cp, "no-check-names", sizeof("no-check-names") - 1)) { statp->options |= RES_NOCHECKNAME; + } else if (!strncmp(cp, "reload-period:", + sizeof("reload-period:") - 1)) { + statp->reload_period = (u_short) + atoi(cp + sizeof("reload-period:") - 1); } #ifdef RES_USE_EDNS0 else if (!strncmp(cp, "edns0", sizeof("edns0") - 1)) { diff --git a/lib/libc/resolv/res_state.c b/lib/libc/resolv/res_state.c index 59c943060757..87643422ebb2 100644 --- a/lib/libc/resolv/res_state.c +++ b/lib/libc/resolv/res_state.c @@ -26,6 +26,8 @@ */ #include +#include +#include #include #include #include @@ -59,13 +61,38 @@ res_keycreate(void) res_thr_keycreated = thr_keycreate(&res_key, free_res) == 0; } +static res_state +res_check_reload(res_state statp) +{ + struct timespec now; + struct stat sb; + + if ((statp->options & RES_INIT) == 0 || statp->reload_period == 0) { + return (statp); + } + + if (clock_gettime(CLOCK_MONOTONIC_FAST, &now) != 0 || + (now.tv_sec - statp->conf_stat) < statp->reload_period) { + return (statp); + } + + statp->conf_stat = now.tv_sec; + if (stat(_PATH_RESCONF, &sb) == 0 && + (sb.st_mtim.tv_sec != statp->conf_mtim.tv_sec || + sb.st_mtim.tv_nsec != statp->conf_mtim.tv_nsec)) { + statp->options &= ~RES_INIT; + } + + return (statp); +} + res_state __res_state(void) { res_state statp; if (thr_main() != 0) - return (&_res); + return res_check_reload(&_res); if (thr_once(&res_init_once, res_keycreate) != 0 || !res_thr_keycreated) @@ -73,7 +100,7 @@ __res_state(void) statp = thr_getspecific(res_key); if (statp != NULL) - return (statp); + return res_check_reload(statp); statp = calloc(1, sizeof(*statp)); if (statp == NULL) return (&_res); diff --git a/share/man/man5/resolver.5 b/share/man/man5/resolver.5 index 4116f23c9cdc..a3c5e05cf7bd 100644 --- a/share/man/man5/resolver.5 +++ b/share/man/man5/resolver.5 @@ -28,7 +28,7 @@ .\" @(#)resolver.5 8.1 (Berkeley) 6/5/93 .\" $FreeBSD$ .\" -.Dd December 25, 2013 +.Dd October 12, 2015 .Dt RESOLVER 5 .Os .Sh NAME @@ -175,6 +175,19 @@ the resolver from obeying the standard and .Sy search rules with the given name. +.It Sy reload-period: Ns Ar n +The resolver checks the modification time of +.Pa /etc/resolv.conf +every +.Ar n +seconds. +If +.Pa /etc/resolv.conf +has changed, it is automatically reloaded. +The default for +.Ar n +is two seconds. +Setting it to zero disables the file check. .El .Pp Options may also be specified as a space or tab separated list using the @@ -191,8 +204,7 @@ If more than one instance of these keywords is present, the last instance will override. .Pp The keyword and value must appear on a single line, and the keyword -(e.g.\& -.Sy nameserver ) +.Pq for example, Sy nameserver must start the line. The value follows the keyword, separated by white space. .Sh FILES