devfs: fix locking and ignore undocumented "fsdev:\n" configuration signature

The confstr was shared between readers so seprintconf() could
write concurrently to that buffer which is not safe.

This replaces the shared static confstr[Maxconf] buffer with a
pointer that is initially nil and a buffer that is alloced on
demand.

The new confstr pointer (and buffer) is now only updated while
wlock()ed from the new setconfstr() function.

This is now done by mconfig() / mdelctl() just before releasing
the wlock.

Now, rdconf() will check if confstr has been initialized, and
test for it again while wlock()ed; making sure the configuration
is read only once.

Also, rdconf() used to check for a undocumented "fsdev:\n" string
at the beginning of config data tho that was never documented.

This changes mconfig() to ignore that particular signature so
the example from the manpage will work as documented.

diff --git a/sys/src/9/port/devfs.c b/sys/src/9/port/devfs.c
index 8efc07e3776de0441ed27bc403da45ee5c77847e..4a75f9c76b508b90802e865291f36a19f1910a24 100644 (file)
--- a/sys/src/9/port/devfs.c
+++ b/sys/src/9/port/devfs.c
@@ -117,12 +117,10 @@ static int qidvers;
 static char *disk;             /* default tree name used */
 static char *source;           /* default inner device used */
 static int sectorsz = Sectorsz;        /* default sector size */
-static char confstr[Maxconf];  /* textual configuration */
+static char *confstr;          /* textual configuration */
 
 static int debug;
 
-static char cfgstr[] = "fsdev:\n";
-
 static Qid tqid = {Qtop, 0, QTDIR};
 static Qid cqid = {Qctl, 0, 0};
 
@@ -180,6 +178,36 @@ seprintdev(char *s, char *e, Fsdev *mp)
        return s;
 }
 
+static char*
+seprintconf(char *s, char *e)
+{
+       int     i, j;
+       Tree    *t;
+
+       *s = 0;
+       for(i = 0; i < ntrees; i++){
+               t = trees[i];
+               if(t != nil)
+                       for(j = 0; j < t->nadevs; j++)
+                               if(t->devs[j] != nil)
+                                       s = seprintdev(s, e, t->devs[j]);
+       }
+       return s;
+}
+
+/* called with lck w */
+static void
+setconfstr(void)
+{
+       char *s;
+
+       s = confstr;
+       if(s == nil)
+               s = smalloc(Maxconf);
+       seprintconf(s, s+Maxconf);
+       confstr = s;
+}
+
 static vlong
 mkpath(int tree, int devno)
 {
@@ -405,6 +433,8 @@ Again:
                        }
                }
        }
+       if(some)
+               setconfstr();
        wunlock(&lck);
        if(some == 0 && alltrees == 0)
                error(Enonexist);
@@ -560,7 +590,11 @@ mconfig(char* a, long n)
        Tree    *t;
 
        /* ignore comments & empty lines */
-       if (*a == '\0' || *a == '#' || *a == '\n')
+       if (n < 1 || *a == '\0' || *a == '#' || *a == '\n')
+               return;
+
+       /* ignore historical config signature */
+       if (n >= 6 && memcmp(a, "fsdev:", 6) == 0)
                return;
 
        dprint("mconfig\n");
@@ -722,8 +756,9 @@ Fail:
        }
        setdsize(mp, ilen);
 
-       poperror();
+       setconfstr();
        wunlock(&lck);
+       poperror();
        free(idev);
        free(ilen);
        free(cb);
@@ -732,21 +767,30 @@ Fail:
 static void
 rdconf(void)
 {
-       int mustrd;
        char *c, *e, *p, *s;
        Chan *cc;
-       static int configed;
+       int mustrd;
 
        /* only read config file once */
-       if (configed)
+       if (confstr != nil)
                return;
-       configed = 1;
 
-       dprint("rdconf\n");
+       wlock(&lck);
+       if (confstr != nil) {
+               wunlock(&lck);
+               return; /* already done */
+       }
+
        /* add the std "fs" tree */
-       trees[0] = &fstree;
-       ntrees++;
-       fstree.name = "fs";
+       if(ntrees == 0){
+               fstree.name = "fs";
+               trees[ntrees++] = &fstree;
+       }
+
+       setconfstr();
+       wunlock(&lck);
+
+       dprint("rdconf\n");
 
        /* identify the config file */
        s = getconf("fsconfig");
@@ -756,7 +800,9 @@ rdconf(void)
        } else
                mustrd = 1;
 
+       c = smalloc(Maxconf+1);
        if(waserror()){
+               free(c);
                if(!mustrd)
                        return;
                nexterror();
@@ -768,23 +814,12 @@ rdconf(void)
                cclose(cc);
                nexterror();
        }
-       devtab[cc->type]->read(cc, confstr, sizeof confstr, 0);
-       poperror();
+       devtab[cc->type]->read(cc, c, Maxconf, 0);
        cclose(cc);
+       poperror();
 
-       /* validate, copy and erase config; mconfig will repopulate confstr */
-       if (strncmp(confstr, cfgstr, sizeof cfgstr - 1) != 0)
-               error("bad #k config, first line must be: 'fsdev:\\n'");
-
-       c = nil;
-       kstrdup(&c, confstr + sizeof cfgstr - 1);
-       if(waserror()){
-               free(c);
-               nexterror();
-       }
-       memset(confstr, 0, sizeof confstr);
        /* process config copy one line at a time */
-       for (p = c; p != nil && *p != '\0'; p = e){
+       for (p = c; *p != '\0'; p = e){
                e = strchr(p, '\n');
                if (e == nil)
                        e = p + strlen(p);
@@ -792,10 +827,9 @@ rdconf(void)
                        e++;
                mconfig(p, e - p);
        }
-       poperror();
-       free(c);
 
-       poperror();     /* mustrd */
+       free(c);
+       poperror();     /* c */
 }
 
 static int
@@ -1138,23 +1172,6 @@ interio(Fsdev *mp, int isread, void *a, long n, vlong off)
        return res;
 }
 
-static char*
-seprintconf(char *s, char *e)
-{
-       int     i, j;
-       Tree    *t;
-
-       *s = 0;
-       for(i = 0; i < ntrees; i++){
-               t = trees[i];
-               if(t != nil)
-                       for(j = 0; j < t->nadevs; j++)
-                               if(t->devs[j] != nil)
-                                       s = seprintdev(s, e, t->devs[j]);
-       }
-       return s;
-}
-
 static long
 mread(Chan *c, void *a, long n, vlong off)
 {
@@ -1175,7 +1192,6 @@ mread(Chan *c, void *a, long n, vlong off)
                goto Done;
        }
        if(c->qid.path == Qctl){
-               seprintconf(confstr, confstr + sizeof(confstr));
                res = readstr((long)off, a, n, confstr);
                goto Done;
        }