UBIFS: incorporate maximum write size

Incorporate maximum write size into the UBIFS description data
structure. This patch just introduces new 'c->max_write_size'
and 'c->max_write_shift' fields as a preparation for the following
patches.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

fs/ubifs/super.c

@@ -507,6 +507,8 @@ static int init_constants_early(struct ubifs_info *c)
 	c->half_leb_size = c->leb_size / 2;
 	c->min_io_size = c->di.min_io_size;
 	c->min_io_shift = fls(c->min_io_size) - 1;
+	c->max_write_size = c->di.max_write_size;
+	c->max_write_shift = fls(c->max_write_size) - 1;
 
 	if (c->leb_size < UBIFS_MIN_LEB_SZ) {
 		ubifs_err("too small LEBs (%d bytes), min. is %d bytes",
@@ -525,6 +527,18 @@ static int init_constants_early(struct ubifs_info *c)
 		return -EINVAL;
 	}
 
+	/*
+	 * Maximum write size has to be greater or equivalent to min. I/O
+	 * size, and be multiple of min. I/O size.
+	 */
+	if (c->max_write_size < c->min_io_size ||
+	    c->max_write_size % c->min_io_size ||
+	    !is_power_of_2(c->max_write_size)) {
+		ubifs_err("bad write buffer size %d for %d min. I/O unit",
+			  c->max_write_size, c->min_io_size);
+		return -EINVAL;
+	}
+
 	/*
 	 * UBIFS aligns all node to 8-byte boundary, so to make function in
 	 * io.c simpler, assume minimum I/O unit size to be 8 bytes if it is
@@ -533,6 +547,10 @@ static int init_constants_early(struct ubifs_info *c)
 	if (c->min_io_size < 8) {
 		c->min_io_size = 8;
 		c->min_io_shift = 3;
+		if (c->max_write_size < c->min_io_size) {
+			c->max_write_size = c->min_io_size;
+			c->max_write_shift = c->min_io_shift;
+		}
 	}
 
 	c->ref_node_alsz = ALIGN(UBIFS_REF_NODE_SZ, c->min_io_size);
@@ -1391,6 +1409,7 @@ static int mount_ubifs(struct ubifs_info *c)
 
 	dbg_msg("compiled on:         " __DATE__ " at " __TIME__);
 	dbg_msg("min. I/O unit size:  %d bytes", c->min_io_size);
+	dbg_msg("max. write size:     %d bytes", c->max_write_size);
 	dbg_msg("LEB size:            %d bytes (%d KiB)",
 		c->leb_size, c->leb_size >> 10);
 	dbg_msg("data journal heads:  %d",