I've been getting a compile error when building the 'next-rc' branch
of btrfs-unstable.
CC fs/btrfs/disk-io.o
fs/btrfs/disk-io.c: In function ‘btree_migratepage’:
fs/btrfs/disk-io.c:716: error: called object ‘0u’ is not a function
make[2]: *** [fs/btrfs/disk-io.o] Error 1
make[1]: *** [fs/btrfs] Error 2
make: *** [fs] Error 2
Line 716 of fs/btrfs/disk-io.c is:
return migrate_page(mapping, newpage, page);
This is related to the "Btrfs: add migrate page for metadata inode"
patch (the first patch in the set of patches added to the next-rc
branch).
When I configure my kernel with CONFIG_MEMORY_HOTPLUG=n, this
automatically unconfigures CONFIG_MIGRATION.
In include/linux/migrate.h, when CONFIG_MIGRATION is not set,
migrate_page is defined as NULL:
/* Possible settings for the migrate_page() method in address_operations */
#define migrate_page NULL
So in this case, migrate_page is defined as NULL instead of as a
function (hence, the "called object is not a function" error).
I've confirmed that setting CONFIG_MEMORY_HOTPLUG=y and
CONFIG_MIGRATION=y is a workaround to clear the error.
As a possible fix, I've wrapped a "#ifdef CONFIG_MIGRATION" statement
around part of the patch, and it seems to be working OK for me. Let
me know if you want this patch submitted as a git patch, although it
might make more sense to fix the original patch since it's still early
in 'next-rc' review period.
$ diff -Nau fs/btrfs/disk-io.c /usr/src/linux/fs/btrfs/disk-io.c
--- fs/btrfs/disk-io.c 2010-11-27 15:59:22.896666675 -0600
+++ /usr/src/linux/fs/btrfs/disk-io.c 2010-11-27 16:08:15.643333349 -0600
@@ -696,6 +696,7 @@
__btree_submit_bio_done);
}
+#ifdef CONFIG_MIGRATION
static int btree_migratepage(struct address_space *mapping,
struct page *newpage, struct page *page)
{
@@ -715,6 +716,9 @@
return migrate_page(mapping, newpage, page);
}
+#else
+#define btree_migratepage NULL
+#endif
static int btree_writepage(struct page *page, struct writeback_control *wbc)
{
--
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