Gitweb:     http://git.kernel.org/linus/5129a469a91a91427334c40e29e64c6d0ab68caf
Commit:     5129a469a91a91427334c40e29e64c6d0ab68caf
Parent:     7e2455c1a123ceadbb35150a610d61e8443fd340
Author:     Jörn Engel <joern@logfs.org>
AuthorDate: Sun Apr 25 08:54:42 2010 +0200
Committer:  Jens Axboe <jens.axboe@oracle.com>
CommitDate: Sun Apr 25 08:54:42 2010 +0200

    Catch filesystems lacking s_bdi
    
    noop_backing_dev_info is used only as a flag to mark filesystems that
    don't have any backing store, like tmpfs, procfs, spufs, etc.
    
    Signed-off-by: Joern Engel <joern@logfs.org>
    
    Changed the BUG_ON() to a WARN_ON(). Note that adding dirty inodes
    to the noop_backing_dev_info is not legal and will not result in
    them being flushed, but we already catch this condition in
    __mark_inode_dirty() when checking for a registered bdi.
    
    Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/super.c                  |    8 +++++---
 fs/sync.c                   |    3 ++-
 include/linux/backing-dev.h |    1 +
 mm/backing-dev.c            |    5 +++++
 4 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index f35ac60..dc72491 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -693,6 +693,7 @@ int set_anon_super(struct super_block *s, void *data)
 		return -EMFILE;
 	}
 	s->s_dev = MKDEV(0, dev & MINORMASK);
+	s->s_bdi = &noop_backing_dev_info;
 	return 0;
 }
 
@@ -954,10 +955,11 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void
 	if (error < 0)
 		goto out_free_secdata;
 	BUG_ON(!mnt->mnt_sb);
+	WARN_ON(!mnt->mnt_sb->s_bdi);
 
- 	error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);
- 	if (error)
- 		goto out_sb;
+	error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);
+	if (error)
+		goto out_sb;
 
 	/*
 	 * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
diff --git a/fs/sync.c b/fs/sync.c
index fc5c3d7..92b2281 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -14,6 +14,7 @@
 #include <linux/pagemap.h>
 #include <linux/quotaops.h>
 #include <linux/buffer_head.h>
+#include <linux/backing-dev.h>
 #include "internal.h"
 
 #define VALID_FLAGS (SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE| \
@@ -32,7 +33,7 @@ static int __sync_filesystem(struct super_block *sb, int wait)
 	 * This should be safe, as we require bdi backing to actually
 	 * write out data in the first place
 	 */
-	if (!sb->s_bdi)
+	if (!sb->s_bdi || sb->s_bdi == &noop_backing_dev_info)
 		return 0;
 
 	if (sb->s_qcop && sb->s_qcop->quota_sync)
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index e19c677..bd0e3c6 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -247,6 +247,7 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
 #endif
 
 extern struct backing_dev_info default_backing_dev_info;
+extern struct backing_dev_info noop_backing_dev_info;
 void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page);
 
 int writeback_in_progress(struct backing_dev_info *bdi);
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index dbda470..707d0dc 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -27,6 +27,11 @@ struct backing_dev_info default_backing_dev_info = {
 };
 EXPORT_SYMBOL_GPL(default_backing_dev_info);
 
+struct backing_dev_info noop_backing_dev_info = {
+	.name		= "noop",
+};
+EXPORT_SYMBOL_GPL(noop_backing_dev_info);
+
 static struct class *bdi_class;
 
 /*
--
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