[PATCH] NOMMU: Improved handling of get_unmapped_area() errors

[David Howells <dhowells@redhat.com>]

The attached patch does two things:

 (1) We no longer check the return value of file->f_op->get_unmapped_area()
     unless we actually called it. We know addr is zero otherwise because
     we'd've given an error earlier if it wasn't.

 (2) If -ENOSYS was returned by that operation, then we assume we actually
     called a driver (such as the framebuffer driver) that might want to
     invoke the operation in a lower level driver (such as matroxfb) if one
     exists, and that it found that one didn't.

     We translate the -ENOSYS error into -ENODEV - the error we would have
     given if the operation was not supplied in the file ops.

     Doing this permits us an opportunity for arch_get_unmapped_area() or
     something else to be called if we want that to happen, particularly in
     the MMU case.

Signed-Off-By: David Howells <dhowells@redhat.com>
---
warthog>diffstat -p1 nommu-2611rc3.diff 
 mm/nommu.c |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diff -uNrp /warthog/kernels/linux-2.6.11-rc3/mm/nommu.c linux-2.6.11-rc3-frv/mm/nommu.c
--- /warthog/kernels/linux-2.6.11-rc3/mm/nommu.c	2005-02-04 11:50:28.000000000 +0000
+++ linux-2.6.11-rc3-frv/mm/nommu.c	2005-02-08 13:54:18.816577889 +0000
@@ -567,12 +567,14 @@ unsigned long do_mmap_pgoff(struct file 
 	 * that it represents a valid section of the address space
 	 * - this is the hook for quasi-memory character devices
 	 */
-	if (file && file->f_op->get_unmapped_area)
+	if (file && file->f_op->get_unmapped_area) {
 		addr = file->f_op->get_unmapped_area(file, addr, len, pgoff, flags);
-
-	if (IS_ERR((void *) addr)) {
-		ret = addr;
-		goto error;
+		if (IS_ERR((void *) addr)) {
+			ret = addr;
+			if (ret == (unsigned long) -ENOSYS)
+				ret = (unsigned long) -ENODEV;
+			goto error;
+		}
 	}
 
 	/* we're going to need a VMA struct as well */