generic_file_aio_read() cleanups

As akpm points out, there's really no need for generic_file_aio_read to
make a special case of count 0: just loop through nr_segs doing nothing.
And as Harvey Harrison points out, there's no need to reset retval to 0
where it's already 0.

Setting count (or ocount) to 0 before calling generic_segment_checks is
unnecessary too; but reluctantly I'll leave that removal to someone with a
wider range of gcc versions to hand - 4.1.2 and 4.2.1 don't warn about it,
but perhaps others do - I forget which are the warniest versions.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Tested-by: Lawrence Greenfield <leg@google.com>
Cc: Christoph Rohland <hans-christoph.rohland@sap.com>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Cc: Zach Brown <zach.brown@oracle.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/filemap.c

@@ -1197,7 +1197,6 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
 
 		mapping = filp->f_mapping;
 		inode = mapping->host;
-		retval = 0;
 		if (!count)
 			goto out; /* skip atime */
 		size = i_size_read(inode);
@@ -1209,33 +1208,30 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
 			}
 			if (retval > 0)
 				*ppos = pos + retval;
-		}
-		if (likely(retval != 0)) {
-			file_accessed(filp);
-			goto out;
+			if (retval) {
+				file_accessed(filp);
+				goto out;
+			}
 		}
 	}
 
-	retval = 0;
-	if (count) {
-		for (seg = 0; seg < nr_segs; seg++) {
-			read_descriptor_t desc;
+	for (seg = 0; seg < nr_segs; seg++) {
+		read_descriptor_t desc;
 
-			desc.written = 0;
-			desc.arg.buf = iov[seg].iov_base;
-			desc.count = iov[seg].iov_len;
-			if (desc.count == 0)
-				continue;
-			desc.error = 0;
-			do_generic_file_read(filp,ppos,&desc,file_read_actor);
-			retval += desc.written;
-			if (desc.error) {
-				retval = retval ?: desc.error;
-				break;
-			}
-			if (desc.count > 0)
-				break;
+		desc.written = 0;
+		desc.arg.buf = iov[seg].iov_base;
+		desc.count = iov[seg].iov_len;
+		if (desc.count == 0)
+			continue;
+		desc.error = 0;
+		do_generic_file_read(filp, ppos, &desc, file_read_actor);
+		retval += desc.written;
+		if (desc.error) {
+			retval = retval ?: desc.error;
+			break;
 		}
+		if (desc.count > 0)
+			break;
 	}
 out:
 	return retval;