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/ioctl.h | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'fs/btrfs/ioctl.h') diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h index b0e73f51d636..85ed35a775b1 100644 --- a/fs/btrfs/ioctl.h +++ b/fs/btrfs/ioctl.h @@ -36,6 +36,14 @@ struct btrfs_ioctl_vol_args { struct btrfs_ioctl_vol_args) #define BTRFS_IOC_SCAN_DEV _IOW(BTRFS_IOCTL_MAGIC, 4, \ struct btrfs_ioctl_vol_args) +/* trans start and trans end are dangerous, and only for + * use by applications that know how to avoid the + * resulting deadlocks + */ +#define BTRFS_IOC_TRANS_START _IO(BTRFS_IOCTL_MAGIC, 6) +#define BTRFS_IOC_TRANS_END _IO(BTRFS_IOCTL_MAGIC, 7) +#define BTRFS_IOC_SYNC _IO(BTRFS_IOCTL_MAGIC, 8) + #define BTRFS_IOC_CLONE _IOW(BTRFS_IOCTL_MAGIC, 9, int) #define BTRFS_IOC_ADD_DEV _IOW(BTRFS_IOCTL_MAGIC, 10, \ struct btrfs_ioctl_vol_args) @@ -43,4 +51,5 @@ struct btrfs_ioctl_vol_args { struct btrfs_ioctl_vol_args) #define BTRFS_IOC_BALANCE _IOW(BTRFS_IOCTL_MAGIC, 12, \ struct btrfs_ioctl_vol_args) + #endif -- cgit v1.2.3