VFS: Implement REQ_BPEEK.

This commit introduces a new request type called REQ_BPEEK. It
requests minor device blocks from the FS.  Analogously to REQ_PEEK,
it requests the filesystem to get the requested blocks into its
cache, without actually copying the result anywhere.

Change-Id: If1d06645b0e17553a64b3167091e9d12efeb3d6f

lib/libminixfs/cache.c

@@ -855,3 +855,33 @@ int lmfs_rdwt_err(void)
 	return rdwt_err;
 }
 
+int lmfs_do_bpeek(message *m)
+{
+	block_t startblock, b, limitblock;
+	dev_t dev = m->REQ_DEV2;
+	u64_t extra, pos = make64(m->REQ_SEEK_POS_LO, m->REQ_SEEK_POS_HI);
+	size_t len = m->REQ_NBYTES;
+	struct buf *bp;
+
+	assert(m->m_type == REQ_BPEEK);
+	assert(fs_block_size > 0);
+	assert(dev != NO_DEV);
+
+	if((extra=(pos % fs_block_size))) {
+		pos -= extra;
+		len += extra;
+	}
+
+	len = roundup(len, fs_block_size);
+
+	startblock = pos/fs_block_size;
+	limitblock = startblock + len/fs_block_size;
+
+	for(b = startblock; b < limitblock; b++) {
+		bp = lmfs_get_block(dev, b, NORMAL);
+		assert(bp);
+		lmfs_put_block(bp, FULL_DATA_BLOCK);
+	}
+
+	return OK;
+}

lib/libpuffs/table.c

@@ -43,4 +43,6 @@ int (*fs_call_vec[])(void) = {
     fs_rdlink,          /* 30  */
     fs_getdents,        /* 31  */
     fs_statvfs,		/* 32  */
+    no_sys,		/* 33 peek */
+    no_sys,		/* 34 bpeek */
 };

lib/libsffs/table.c

@@ -42,6 +42,7 @@ int (*call_vec[])(void) = {
 	do_getdents,	/* 31 getdents		*/
 	do_statvfs,	/* 32 statvfs		*/
 	no_sys,		/* 33 peek		*/
+	no_sys,		/* 33 bpeek		*/
 };
 
 /* This should not fail with "array size is negative": */

lib/libvtreefs/table.c

@@ -38,6 +38,7 @@ int (*fs_call_vec[])(void) = {
 	fs_getdents,	/* 31	getdents	*/
 	fs_statvfs,	/* 32	statvfs		*/
 	no_sys,		/* 33   peek            */
+	no_sys,		/* 34   bpeek           */
 };
 
 /* This should not fail with "array size is negative": */