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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>
56 lines
1.9 KiB
C
56 lines
1.9 KiB
C
/*
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* Copyright (C) 2007 Oracle. All rights reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public
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* License v2 as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public
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* License along with this program; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 021110-1307, USA.
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*/
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#ifndef __IOCTL_
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#define __IOCTL_
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#include <linux/ioctl.h>
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#define BTRFS_IOCTL_MAGIC 0x94
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#define BTRFS_VOL_NAME_MAX 255
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#define BTRFS_PATH_NAME_MAX 4095
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struct btrfs_ioctl_vol_args {
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char name[BTRFS_PATH_NAME_MAX + 1];
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};
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#define BTRFS_IOC_SNAP_CREATE _IOW(BTRFS_IOCTL_MAGIC, 1, \
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struct btrfs_ioctl_vol_args)
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#define BTRFS_IOC_DEFRAG _IOW(BTRFS_IOCTL_MAGIC, 2, \
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struct btrfs_ioctl_vol_args)
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#define BTRFS_IOC_RESIZE _IOW(BTRFS_IOCTL_MAGIC, 3, \
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struct btrfs_ioctl_vol_args)
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#define BTRFS_IOC_SCAN_DEV _IOW(BTRFS_IOCTL_MAGIC, 4, \
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struct btrfs_ioctl_vol_args)
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/* trans start and trans end are dangerous, and only for
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* use by applications that know how to avoid the
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* resulting deadlocks
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*/
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#define BTRFS_IOC_TRANS_START _IO(BTRFS_IOCTL_MAGIC, 6)
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#define BTRFS_IOC_TRANS_END _IO(BTRFS_IOCTL_MAGIC, 7)
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#define BTRFS_IOC_SYNC _IO(BTRFS_IOCTL_MAGIC, 8)
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#define BTRFS_IOC_CLONE _IOW(BTRFS_IOCTL_MAGIC, 9, int)
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#define BTRFS_IOC_ADD_DEV _IOW(BTRFS_IOCTL_MAGIC, 10, \
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struct btrfs_ioctl_vol_args)
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#define BTRFS_IOC_RM_DEV _IOW(BTRFS_IOCTL_MAGIC, 11, \
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struct btrfs_ioctl_vol_args)
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#define BTRFS_IOC_BALANCE _IOW(BTRFS_IOCTL_MAGIC, 12, \
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struct btrfs_ioctl_vol_args)
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#endif
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