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| author | Sage Weil <sage@newdream.net> | 2008-06-10 10:07:39 -0400 |
|---|---|---|
| committer | Chris Mason <chris.mason@oracle.com> | 2008-09-25 11:04:03 -0400 |
| commit | 6bf13c0cc833bf5ba013d6aa60379484bf48c4e6 (patch) | |
| tree | ae2b54a1a26a89fece49f6b6d6dff8448efab542 /fs/btrfs/ioctl.h | |
| parent | eba12c7bfcb4855fc757357e5e5b0b9a474499ba (diff) | |
| download | lwn-6bf13c0cc833bf5ba013d6aa60379484bf48c4e6.tar.gz lwn-6bf13c0cc833bf5ba013d6aa60379484bf48c4e6.zip | |
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.h | 9 |
1 files changed, 9 insertions, 0 deletions
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 |