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fs: skip adm messages when fs is readonly

small but harmless race -- we may flip rdonly while
enqueueing a message, which may lead to a spurious
message print.

--- a/fs.c

+++ b/fs.c

@@ -2207,6 +2207,10 @@

 		sysfatal("malloc log heads");

 	while(1){

 		am = chrecv(fs->admchan);

+		if(fs->rdonly){

+			fprint(2, "spurious adm message\n");

+			break;

+		}

 		switch(am->op){

 		case AOsync:

 			if(waserror()){

@@ -2291,6 +2295,7 @@

 			if(waserror()){

 				fprint(2, "clear file %llx: %s\n", am->qpath, errmsg());

 				ainc(&fs->rdonly);

+				break;

 			}

 			for(off = am->off; off < am->length; off += Blksz){

 				qlock(&fs->mutlk);

@@ -2357,9 +2362,11 @@

 	tmnow(&then, nil);

 	tmnow(&now, nil);

 	while(1){

+		sleep(5000);

+		if(fs->rdonly)

+			continue;

 		if(waserror())

 			fprint(2, "task error: %s", errmsg());

-		sleep(5000);

 		a = emalloc(sizeof(Amsg), 1);

 		a->op = AOsync;

 		a->halt = 0;

--- a/load.c

+++ b/load.c

@@ -64,7 +64,9 @@

 	Arena *a;

 	Bptr bp;

 	Tree *t;

+	Dir *d;

 	int i, k;

+	vlong eb;

 	if((dump = mallocz(sizeof(*dump), 1)) == nil)

 		sysfatal("malloc: %r");

@@ -80,10 +82,16 @@

 	fs->narena = 1;

 	if((fs->fd = open(dev, ORDWR)) == -1)

 		sysfatal("open %s: %r", dev);

+	if((d = dirfstat(fs->fd)) == nil)

+		sysfatal("stat %s: %r", dev);

+

+	eb = d->length - (d->length%Blksz) - Blksz;

 	bp = (Bptr){0, -1, -1};

 	fs->sb0 = getblk(bp, GBnochk);

-	bp = (Bptr){512*MiB, -1, -1};

+	bp = (Bptr){eb, -1, -1};

 	fs->sb1 = getblk(bp, GBnochk);

+	free(d);

+

 	unpacksb(fs, fs->sb0->buf, Blksz);

 	if((fs->arenas = calloc(fs->narena, sizeof(Arena))) == nil)

 		sysfatal("malloc: %r");

--- a/ream.c

+++ b/ream.c

@@ -168,10 +168,6 @@

 	Blk *b, *hd, *tl;

 	b = cachepluck();

-	if(start == 512*MiB){

-		start += Blksz;

-		asz -= Blksz;

-	}

 	addr = start+Blksz;	/* leave room for arena hdr */

 	a->loghd.addr = -1;

@@ -181,10 +177,6 @@

 	memset(b->buf, 0, sizeof(b->buf));

 	b->type = Tlog;

 	b->bp.addr = addr+Blksz;

-	if(b->bp.addr == 512*MiB){

-		b->bp.addr += Blksz;

-		asz -= Blksz;

-	}

 	b->logsz = 0;

 	b->logp = (Bptr){-1, -1, -1};

 	b->data = b->buf + Loghdsz;

@@ -196,11 +188,6 @@

 	PACK64(p, asz-Blksz);		p += 8;	/* len */

 	PACK64(p, b->bp.addr|LogAlloc);	p += 8;	/* addr */

 	PACK64(p, Blksz);		p += 8;	/* len */

-	/* backup sb */

-	if(start <= 512*MiB && start+asz > 512*MiB){

-		PACK64(p, (512*MiB)|LogAlloc1);

-		p += 8;

-	}

 	PACK64(p, (uvlong)LogSync);	p += 8;	/* barrier */

 	b->logsz = p - b->data;

 	finalize(b);

@@ -261,8 +248,6 @@

 	sz = d->length;

 	free(d);

-	if(sz < 512*MiB+Blksz)

-		sysfatal("ream: disk too small");

 	mnt = emalloc(sizeof(Mount), 1);

 	mnt->root = mallocz(sizeof(Tree), 1);

 	adm = mallocz(sizeof(Mount), 1);

@@ -286,7 +271,7 @@

 	sb0 = cachepluck();

 	sb1 = cachepluck();

 	sb0->bp = (Bptr){0, -1, -1};

-	sb1->bp = (Bptr){512*MiB, -1, -1};

+	sb1->bp = (Bptr){sz+Blksz, -1, -1};

 	fs->arenabp = emalloc(fs->narena * sizeof(Bptr), 1);

 	for(i = 0; i < fs->narena; i++){