GitHub-Mirror/Star64_linux
2
0
Fork 0
mirror of https://github.com/Fishwaldo/Star64_linux.git synced 2025-06-23 07:01:23 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions

Btrfs: transaction ioctls

Browse source 
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>
This commit is contained in:
Sage Weil 2008-06-10 10:07:39 -04:00 • committed by Chris Mason
parent eba12c7bfc
commit 6bf13c0cc8
5 changed files with 83 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

9
fs/btrfs/ioctl.h
View file

@ -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