libminixfs: allow non-pagesize-multiple FSes

The memory-mapped files implementation (mmap() etc.) is implemented with
the help of the filesystems using the in-VM FS cache. Filesystems tell it
about all cached blocks and their metadata. Metadata is: device offset and,
if any (and known), inode number and in-inode offset. VM can then map in
requested memory-mapped file blocks, and request them if necessary.

A limitation of this system is that filesystem block sizes that are not
a multiple of the VM system (and VM hardware) page size are not possible;
we can't map blocks in partially. (We can copy, but then the benefits of
mapping and sharing the physical pages is gone.) So until before this
commit various pieces of caching code assumed page size multiple
blocksizes. This isn't strictly necessary as long as mmap() needn't be
supported on that FS.

This change allows the in-FS cache code (libminixfs) to allocate any-sized
blocks, and will not interact with the VM cache for non-pagesize-multiple
blocks. In that case it will also signal requestors, by failing 'peek'
requests, that mmap() should not be supported on this FS. VM and VFS
will then gracefully fail all file-mapping mmap() calls, and exec() will
fall back to copying executable blocks instead of mmap()ping executables.

As a result, 3 diagnostics that signal file-mapped mmap()s failing
(hitherto an unusual occurence) are disabled, as ld.so does file-mapped
mmap()s to map in objects it needs. On FSes not supporting it this situation
is legitimate and shouldn't cause so much noise. ld.so will revert to its own
minix-specific allocate+copy style of starting executables if mmap()s fail.

Change-Id: Iecb1c8090f5e0be28da8f5181bb35084eb18f67b

lib/libminixfs/cache.c

@@ -161,8 +161,12 @@ free_unused_blocks(void)
 static void
 lmfs_alloc_block(struct buf *bp)
 {
+  int len;
   ASSERT(!bp->data);
   ASSERT(bp->lmfs_bytes == 0);
+
+  len = roundup(fs_block_size, PAGE_SIZE);
+
   if((bp->data = minix_mmap(0, fs_block_size,
      PROT_READ|PROT_WRITE, MAP_PREALLOC|MAP_ANON, -1, 0)) == MAP_FAILED) {
 	free_unused_blocks();
@@ -191,9 +195,12 @@ void minix_munmap_t(void *a, int len)
 	assert(a);
 	assert(a != MAP_FAILED);
 	assert(len > 0);
-	assert(!(len % PAGE_SIZE));
 	assert(!(av % PAGE_SIZE));
 
+	len = roundup(len, PAGE_SIZE);
+
+	assert(!(len % PAGE_SIZE));
+
 	if(minix_munmap(a, len) < 0)
 		panic("libminixfs cache: munmap failed");
 }
@@ -513,17 +520,19 @@ register struct buf *bp;	/* buffer pointer */
   pos = mul64u(bp->lmfs_blocknr, fs_block_size);
   if(fs_block_size > PAGE_SIZE) {
 #define MAXPAGES 20
-	vir_bytes vaddr = (vir_bytes) bp->data;
-	int p;
+	vir_bytes blockrem, vaddr = (vir_bytes) bp->data;
+	int p = 0;
   	static iovec_t iovec[MAXPAGES];
-	int pages = fs_block_size/PAGE_SIZE;
-	ASSERT(pages > 1 && pages < MAXPAGES);
-	for(p = 0; p < pages; p++) {
+	blockrem = fs_block_size;
+	while(blockrem > 0) {
+		vir_bytes chunk = blockrem >= PAGE_SIZE ? PAGE_SIZE : blockrem;
 		iovec[p].iov_addr = vaddr;
-		iovec[p].iov_size = PAGE_SIZE;
-		vaddr += PAGE_SIZE;
+		iovec[p].iov_size = chunk;
+		vaddr += chunk;
+		blockrem -= chunk;
+		p++;
 	}
-  	r = bdev_gather(dev, pos, iovec, pages, BDEV_NOFLAGS);
+  	r = bdev_gather(dev, pos, iovec, p, BDEV_NOFLAGS);
   } else {
   	r = bdev_read(dev, pos, bp->data, fs_block_size,
   		BDEV_NOFLAGS);
@@ -638,9 +647,9 @@ void lmfs_rw_scattered(
   }
 
   assert(dev != NO_DEV);
-  assert(!(fs_block_size % PAGE_SIZE));
   assert(fs_block_size > 0);
-  iov_per_block = fs_block_size / PAGE_SIZE;
+  iov_per_block = roundup(fs_block_size, PAGE_SIZE) / PAGE_SIZE;
+  assert(iov_per_block < NR_IOREQS);
   
   /* (Shell) sort buffers on lmfs_blocknr. */
   gap = 1;
@@ -669,19 +678,24 @@ void lmfs_rw_scattered(
 	int r;
 	for (iop = iovec; nblocks < bufqsize; nblocks++) {
 		int p;
-		vir_bytes vdata;
+		vir_bytes vdata, blockrem;
 		bp = bufq[nblocks];
 		if (bp->lmfs_blocknr != (block_t) bufq[0]->lmfs_blocknr + nblocks)
 			break;
 		if(niovecs >= NR_IOREQS-iov_per_block) break;
 		vdata = (vir_bytes) bp->data;
+		blockrem = fs_block_size;
 		for(p = 0; p < iov_per_block; p++) {
+			vir_bytes chunk = blockrem < PAGE_SIZE ? blockrem : PAGE_SIZE;
 			iop->iov_addr = vdata;
-			iop->iov_size = PAGE_SIZE;
+			iop->iov_size = chunk;
 			vdata += PAGE_SIZE;
+			blockrem -= chunk;
 			iop++;
 			niovecs++;
 		}
+		assert(p == iov_per_block);
+		assert(blockrem == 0);
 	}
 
 	assert(nblocks > 0);
@@ -825,7 +839,7 @@ void lmfs_set_blocksize(int new_block_size, int major)
 
   vmcache = 0;
 
-  if(may_use_vmcache)
+  if(may_use_vmcache && !(new_block_size % PAGE_SIZE))
 	vmcache = 1;
 }
 
@@ -932,6 +946,10 @@ int lmfs_do_bpeek(message *m)
 	assert(fs_block_size > 0);
 	assert(dev != NO_DEV);
 
+	if(!vmcache) { return ENXIO; }
+
+	assert(!(fs_block_size % PAGE_SIZE));
+
 	if((extra=(pos % fs_block_size))) {
 		pos -= extra;
 		len += extra;

servers/vfs/misc.c

@@ -327,7 +327,9 @@ int dupvm(struct fproc *rfp, int pfd, int *vmfd, struct filp **newfilp)
 
 	if(!f->filp_vno->v_vmnt->m_haspeek) {
 		unlock_filp(f);
+#if 0	/* Noisy diagnostic for mmap() by ld.so */
 		printf("VFS dupvm: no peek available\n");
+#endif
 		return EINVAL;
 	}
 
@@ -409,7 +411,9 @@ int do_vm_call(message *m_out)
 			}
 
 			if((result = dupvm(rfp, req_fd, &procfd, &f)) != OK) {
+#if 0   /* Noisy diagnostic for mmap() by ld.so */
 				printf("vfs: dupvm failed\n");
+#endif
 				goto reqdone;
 			}
 

servers/vm/mmap.c

@@ -180,8 +180,10 @@ static void mmap_file_cont(struct vmproc *vmp, message *replymsg, void *cbarg,
 		writable = 1;
 
 	if(replymsg->VMV_RESULT != OK) {
+#if 0   /* Noisy diagnostic for mmap() by ld.so */
 		printf("VM: VFS reply failed (%d)\n", replymsg->VMV_RESULT);
 		sys_sysctl_stacktrace(vmp->vm_endpoint);
+#endif
 		result = origmsg->VMV_RESULT;
 	} else {
 		/* Finish mmap */