Many years ago, I asked on this list if it was possible to change the precedence order of exports listed in /etc/exports where there is more than one possible match (see the thread at: https://marc.info/?l=linux-nfs&m=130565040627856&w=2) - and answer was 'No' At that time, I used a simple hack to force the precedence order I required (by modifying the 'MCL' enum order in nfs-utils support/include/exportfs.h) However, the issue has come up again for me, so I thought I would see if I could alter the precedence order by adding an exports 'priority=' option as suggested later in the above thread I started with the nfs-utils supplied with CentOS 7 (based on 1.3.0) - and added logic to lookup_export() to check for client specifications with a higher priority - but this didn't work - so looking for other places that looped through MCL types, I added similar logic in nfsd_fh() - which seems to work as I expected (I'm using NFSv3) However, adding similar logic to the nfs-utils supplied with Rocky 9 (based on 2.5.4) didn't work ... But comparing the code in nfsd_fh() in v1.3.0 and nfsd_handle_fh() in v2.5.4, nfsd_fh() in v1.3.0 does the following towards the end of the function - whereas nfsd_handle_fh() in v2.5.4 doesn't: if (cache_export_ent(buf, sizeof(buf), dom, found, found_path) < 0) found = 0; By adding the above lines at a similar place in nfsd_handle_fh() in v2.5.4, seems to 'fix' the issue and all works as I expected I don't fully understand what is going on under the hood with all this, so no idea if what I've done is 'correct', or if there is a better way of doing what I'm trying to achieve ? Below is a patch (made against the latest git nfs-utils) of what I've done - could anyone let me know if I'm going along the right lines (or not) ? (I apologize if the formatting of the patch gets mangled by Gmail) Thanks James Pearson diff --git a/support/export/cache.c b/support/export/cache.c index 6c0a44a3..e9392d8e 100644 --- a/support/export/cache.c +++ b/support/export/cache.c @@ -54,6 +54,8 @@ enum nfsd_fsid { FSID_UUID16_INUM, }; +static int cache_export_ent(char *buf, int buflen, char *domain, struct exportent *exp, char *path); + #undef is_mountpoint static int is_mountpoint(const char *path) { @@ -877,6 +879,14 @@ static int nfsd_handle_fh(int f, char *bp, int blen) xlog(L_WARNING, "%s and %s have same filehandle for %s, using first", found_path, path, dom); } else { + /* same path, see if this one has a higher export priority */ + if (exp->m_export.e_priority > found->e_priority) { + found = &exp->m_export; + free(found_path); + found_path = strdup(path); + if (found_path == NULL) + goto out; + } /* same path, if one is V4ROOT, choose the other */ if (found->e_flags & NFSEXP_V4ROOT) { found = &exp->m_export; @@ -910,6 +920,12 @@ static int nfsd_handle_fh(int f, char *bp, int blen) goto out; } + /* adding this here - to make sure priority export changes are + * picked up (this used to be in 1.X versions ?) + */ + if (cache_export_ent(buf, sizeof(buf), dom, found, found_path) < 0) + found = 0; + bp = buf; blen = sizeof(buf); qword_add(&bp, &blen, dom); qword_addint(&bp, &blen, fsidtype); @@ -1178,6 +1194,12 @@ lookup_export(char *dom, char *path, struct addrinfo *ai) found_type = i; continue; } + /* see if this one has a higher export priority */ + if (exp->m_export.e_priority > found->m_export.e_priority) { + found = exp; + found_type = i; + continue; + } /* Always prefer non-V4ROOT exports */ if (exp->m_export.e_flags & NFSEXP_V4ROOT) continue; diff --git a/support/include/nfslib.h b/support/include/nfslib.h index eff2a486..ab22ecaf 100644 --- a/support/include/nfslib.h +++ b/support/include/nfslib.h @@ -99,6 +99,7 @@ struct exportent { unsigned int e_ttl; char * e_realpath; int e_reexport; + int e_priority; }; struct rmtabent { diff --git a/support/nfs/exports.c b/support/nfs/exports.c index a6816e60..548063b8 100644 --- a/support/nfs/exports.c +++ b/support/nfs/exports.c @@ -374,6 +374,9 @@ putexportent(struct exportent *ep) fprintf(fp, "%d,", id[i]); } fprintf(fp, "anonuid=%d,anongid=%d", ep->e_anonuid, ep->e_anongid); + if (ep->e_priority) { + fprintf(fp, ",priority=%d", ep->e_priority); + } secinfo_show(fp, ep); xprtsecinfo_show(fp, ep); fprintf(fp, ")\n"); @@ -834,6 +837,14 @@ bad_option: setflags(NFSEXP_FSID, active, ep); saw_reexport = 1; + } else if (strncmp(opt, "priority=", 9) == 0) { + char *oe; + ep->e_priority = strtol(opt+9, &oe, 10); + if (opt[9]=='\0' || *oe != '\0') { + xlog(L_ERROR, "%s: %d: bad priority \"%s\"\n", + flname, flline, opt); + goto bad_option; + } } else { xlog(L_ERROR, "%s:%d: unknown keyword \"%s\"\n", flname, flline, opt);
