From 6bf13c0cc833bf5ba013d6aa60379484bf48c4e6 Mon Sep 17 00:00:00 2001 From: Sage Weil Date: Tue, 10 Jun 2008 10:07:39 -0400 Subject: Btrfs: transaction ioctls These ioctls let a user application hold a transaction open while it performs a series of operations. A final ioctl does a sync on the fs (closing the current transaction). This is the main requirement for Ceph's OSD to be able to keep the data it's storing in a btrfs volume consistent, and AFAICS it works just fine. The application would do something like fd = ::open("some/file", O_RDONLY); ::ioctl(fd, BTRFS_IOC_TRANS_START); /* do a bunch of stuff */ ::ioctl(fd, BTRFS_IOC_TRANS_END); or just ::close(fd); And to ensure it commits to disk, ::ioctl(fd, BTRFS_IOC_SYNC); When a transaction is held open, the trans_handle is attached to the struct file (via private_data) so that it will get cleaned up if the process dies unexpectedly. A held transaction is also ended on fsync() to avoid a deadlock. A misbehaving application could also deliberately hold a transaction open, effectively locking up the FS, so it may make sense to restrict something like this to root or something. Signed-off-by: Chris Mason --- fs/btrfs/super.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fs/btrfs/super.c') diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c index 77f44494e229..39bb86945ed0 100644 --- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -293,7 +293,7 @@ fail_close: return err; } -static int btrfs_sync_fs(struct super_block *sb, int wait) +int btrfs_sync_fs(struct super_block *sb, int wait) { struct btrfs_trans_handle *trans; struct btrfs_root *root; -- cgit v1.2.3