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authorSage Weil <sage@newdream.net>2008-06-10 10:07:39 -0400
committerChris Mason <chris.mason@oracle.com>2008-09-25 11:04:03 -0400
commit6bf13c0cc833bf5ba013d6aa60379484bf48c4e6 (patch)
treeae2b54a1a26a89fece49f6b6d6dff8448efab542 /fs/btrfs/ioctl.h
parenteba12c7bfcb4855fc757357e5e5b0b9a474499ba (diff)
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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 <chris.mason@oracle.com>
Diffstat (limited to 'fs/btrfs/ioctl.h')
-rw-r--r--fs/btrfs/ioctl.h9
1 files changed, 9 insertions, 0 deletions
diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
index b0e73f5..85ed35a 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
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