Message ID | 541082E0.8050707@redhat.com |
---|---|
State | Not applicable |
Headers |
Received: (qmail 28733 invoked by alias); 10 Sep 2014 16:57:09 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: <libc-alpha.sourceware.org> List-Unsubscribe: <mailto:libc-alpha-unsubscribe-##L=##H@sourceware.org> List-Subscribe: <mailto:libc-alpha-subscribe@sourceware.org> List-Archive: <http://sourceware.org/ml/libc-alpha/> List-Post: <mailto:libc-alpha@sourceware.org> List-Help: <mailto:libc-alpha-help@sourceware.org>, <http://sourceware.org/ml/#faqs> Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 28723 invoked by uid 89); 10 Sep 2014 16:57:09 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-3.9 required=5.0 tests=AWL, BAYES_00, RP_MATCHES_RCVD, SPF_HELO_PASS, SPF_PASS autolearn=ham version=3.3.2 X-HELO: mx1.redhat.com Message-ID: <541082E0.8050707@redhat.com> Date: Wed, 10 Sep 2014 12:57:04 -0400 From: "Carlos O'Donell" <carlos@redhat.com> User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.7.0 MIME-Version: 1.0 To: Siddhesh Poyarekar <siddhesh@redhat.com> CC: Michael Kerrisk <mtk.manpages@gmail.com>, "linux-man@vger.kernel.org" <linux-man@vger.kernel.org>, Simo Sorce <ssorce@redhat.com>, Jakub Hrozek <jhrozek@redhat.com>, GNU C Library <libc-alpha@sourceware.org> Subject: Re: [PATCH] getgrent.3: Add ENOENT to error list. References: <54105ED1.5020206@redhat.com> <20140910145307.GC14885@spoyarek.pnq.redhat.com> In-Reply-To: <20140910145307.GC14885@spoyarek.pnq.redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit |
Commit Message
Carlos O'Donell
Sept. 10, 2014, 4:57 p.m. UTC
On 09/10/2014 10:53 AM, Siddhesh Poyarekar wrote: > On Wed, Sep 10, 2014 at 10:23:13AM -0400, Carlos O'Donell wrote: >> It's possible to get ENOENT returned from getgrent >> if the backend, for example say SSSD, isn't configured >> or the daemon isn't running. The same can be said of any >> of the NSS backend. > > The daemon not running is internally a NSS_STATUS_TRYAGAIN + > EAGAIN[1], i.e. that is what the sssd nss plugin should return to > glibc. glibc then should return that as a NOTFOUND, which for > getgrent is a NULL return without errno set. I don't see why ENOENT > is necessary. This is orthogonal to the discussion at hand. At present glibc will return a NULL `struct group*' and errno set to ENOENT if the NSS plugin returns NSS_STATUS_UNAVAIL and errno ENOENT indicating it is incorrectly configured. This is a documented entry in the glibc manual, and is presently how SSSD behaves (until it gets fixed). Wether we like it or not there is a present day distinction between "permanently unavailable until an admin fixes it" (NSS_STATUS_UNAVAIL,ENOENT), "temporarily unavailable" (NSS_STATUS_TRYAGAIN,EAGAIN), and the former may be seen by the user, and may be useful to act upon by a program that is interested in that behaviour. I do not think glibc should hide NSS_STATUS_TRYAGAIN from the user. To be clear ENOENT is neccessary if you want to actually detect that something is wrong with your system and take evasive action. Simply getting back no results is not sufficient to take corrective action. In the case of sss however the intent of the inactive plugin is to operate as if it had no data. At least this is what I've been told by those working on SSSD at Red Hat. SSSD should *not* use status==NSS_STATUS_TRYAGAIN and errno==EAGAIN because that will simply result in EAGAIN being returned to userspace from getgrent which is again a deviation from the entire philosophy behind SSSD wanting `sss` in nsswitch.conf. The point is to appear as a transparent plugin that is enabled at a later time by starting up the daemon. For example if you fix SSSD to use status==NSS_STATUS_TRYAGIN errno==EAGAIN instead you get this still wrong behaviour from this test case: #include <stdio.h> #include <stdlib.h> #include <errno.h> #include <grp.h> int main(int argc, char *argv[]) { struct group *p_group; setgrent(); while (1) { errno = 0; /* initialize for getgrent() */ p_group = getgrent(); if (p_group == NULL) { if (errno == 0) { break; /* end of groups */ } else { perror("getgrent"); /* error occurs. */ printf("getgrent error %d \n", errno); endgrent(); exit(-2); } } printf("getgrent() OK group(%d) = %s \n",p_group->gr_gid, p_group->gr_name); } exit(0); } With SSSD using status==NSS_STATUS_TRYAGAIN errno==EAGAIN: getgrent() OK group(0) = root getgrent() OK group(1) = bin getgrent() OK group(2) = daemon ... getgrent: Resource temporarily unavailable getgrent error 11 With SSSD using status==NSS_STATUS_UNAVAIL errno==ENOENT: getgrent() OK group(0) = root getgrent() OK group(1) = bin getgrent() OK group(2) = daemon ... getgrent: No such file or directory getgrent error 2 With SSSD using status==NSS_STATUS_NOTFOUND errno==0: getgrent() OK group(0) = root getgrent() OK group(1) = bin getgrent() OK group(2) = daemon getgrent() OK group(3) = sys ... getgrent() OK group(185) = wildfly Which completes successfully and is the only way it should work for an installed SSSD nss module. e.g. --- Please correct me if you think something I've said is wrong or doesn't make sense. Cheers, Carlos.
Comments
On Wed, Sep 10, 2014 at 12:57:04PM -0400, Carlos O'Donell wrote: > At present glibc will return a NULL `struct group*' and errno set to > ENOENT if the NSS plugin returns NSS_STATUS_UNAVAIL and errno ENOENT > indicating it is incorrectly configured. This is a documented entry > in the glibc manual, and is presently how SSSD behaves (until it > gets fixed). Yes but the entry in the libc manual documents the interface between the plugin and glibc, not the plugin and the user or glibc and the user. > Wether we like it or not there is a present day distinction between > "permanently unavailable until an admin fixes it" (NSS_STATUS_UNAVAIL,ENOENT), > "temporarily unavailable" (NSS_STATUS_TRYAGAIN,EAGAIN), and the former > may be seen by the user, and may be useful to act upon by a program > that is interested in that behaviour. I do not think glibc should hide > NSS_STATUS_TRYAGAIN from the user. > > To be clear ENOENT is neccessary if you want to actually detect that > something is wrong with your system and take evasive action. Simply > getting back no results is not sufficient to take corrective action. > In the case of sss however the intent of the inactive plugin is to > operate as if it had no data. At least this is what I've been told by > those working on SSSD at Red Hat. > > SSSD should *not* use status==NSS_STATUS_TRYAGAIN and errno==EAGAIN > because that will simply result in EAGAIN being returned to userspace > from getgrent which is again a deviation from the entire philosophy > behind SSSD wanting `sss` in nsswitch.conf. The point is to appear > as a transparent plugin that is enabled at a later time by starting > up the daemon. This seems to me to be a case for the nss subsystem to clear errno if it does not. I'd read the errno list as the number of ways it is allowed to fail extraordinarily and a resource not being available is currently not considered as an extraordinary failure by POSIX. So in that context it is a bug in the nss subsystem. My point is that we'll be deviating from the standard by supporting an extra way to fail and maybe we should get some kind of clarification from the Austin group before simply documenting it as the truth. Siddhesh
diff -urN sssd-1.11.6/src/sss_client/nss_group.c sssd-1.11.6.mod/src/sss_client/nss_group.c --- sssd-1.11.6/src/sss_client/nss_group.c 2014-06-03 10:31:33.000000000 -0400 +++ sssd-1.11.6.mod/src/sss_client/nss_group.c 2014-09-10 12:21:52.330685026 -0400 @@ -539,6 +539,11 @@ if (nret != NSS_STATUS_SUCCESS) { errno = errnop; } + /* Always pretend we have no data. */ + if (nret == NSS_STATUS_UNAVAIL) { + nret = NSS_STATUS_NOTFOUND; + errno = 0; + } sss_nss_unlock(); return nret; @@ -639,6 +644,11 @@ if (nret != NSS_STATUS_SUCCESS) { errno = errnop; } + /* Always pretend we have no data. */ + if (nret == NSS_STATUS_UNAVAIL) { + nret = NSS_STATUS_NOTFOUND; + errno = 0; + } sss_nss_unlock(); return nret;