fstrans(9) - NetBSD Manual Pages

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FSTRANS(9)             NetBSD Kernel Developer's Manual             FSTRANS(9)


NAME
fstrans, fstrans_setstate, fstrans_getstate, fstrans_start, fstrans_start_nowait, fstrans_done, fstrans_is_owner, fscow_establish, fscow_disestablish, fscow_run -- file system suspension helper subsystem
SYNOPSIS
#include <sys/mount.h> #include <sys/fstrans.h> int fstrans_setstate(struct mount *mp, enum fstrans_state new_state); enum fstrans_state fstrans_getstate(struct mount *mp); void fstrans_start(struct mount *mp, enum fstrans_lock_type lock_type); int fstrans_start_nowait(struct mount *mp, enum fstrans_lock_type lock_type); void fstrans_done(struct mount *mp); int fstrans_is_owner(struct mount *mp); int fscow_establish(struct mount *mp, int (*func)(void *, struct buf *, bool), void *cookie); int fscow_disestablish(struct mount *mp, int (*func)(void *, struct buf *, bool), void *cookie); int fscow_run(struct buf *bp, bool data_valid);
DESCRIPTION
The fstrans subsystem is a set of operations to assist file system sus- pension. These operations must not be used outside of file systems. File systems supporting this subsystem must set the flag IMNT_HAS_TRANS in mnt_iflag. File systems are always in one of these states: FSTRANS_NORMAL normal operations. FSTRANS_SUSPENDING preparing a suspension. FSTRANS_SUSPENDED suspended. This state is represented by enum fstrans_state. fstrans_getstate(mp) returns the current state of the file system mp. fstrans_setstate(mp, new_state) changes the state of the file system mp to new_state. All file system operations use a fstrans lock. This lock is recursive. A thread already owning a lock will always get another lock. The lock has two variants: FSTRANS_SHARED this lock will be granted if the file system is in state FSTRANS_NORMAL. FSTRANS_LAZY this lock will be granted if the file system is in state FSTRANS_NORMAL or FSTRANS_SUSPENDING. It needs special care because operations using this variant will not block while the file system pre- pares suspension. The lock variant is represented by enum fstrans_lock_type. fstrans_start(mp, lock_type) sets a lock of type lock_type on the file system mp. fstrans_start_nowait(mp, lock_type) will not wait for a state change of the file system when attempting to aquire the lock. The thread may still sleep while attempting to aquire the lock. fstrans_done(mp) releases a lock on the file system mp. fstrans_is_owner(mp) returns true if this thread is currently suspending the file system mp. fscow_establish(mp, func, cookie) Establish a copy-on-write callback for the file system mp. func will be called for every buffer written through this file sys- tem. fscow_disestablish(mp, func, cookie) Disestablish a copy-on-write callback registered with fscow_establish(). fscow_run(bp, data_valid) Run all copy-on-write callbacks established for the file system this buffer belongs to. If data_valid is true the buffer data has not yet been modified.
RETURN VALUES
The functions fstrans_setstate() and fstrans_start_nowait() return zero on success and an error value on failure.
EXAMPLES
The following is an example of a file system suspend operation. int xxx_suspendctl(struct mount *mp, int cmd) { int error; switch (cmd) { case SUSPEND_SUSPEND: error = fstrans_setstate(mp, FSTRANS_SUSPENDING); if (error != 0) return error; /* Sync file system state to disk. */ return fstrans_setstate(mp, FSTRANS_SUSPENDED); case SUSPEND_RESUME: return fstrans_setstate(mp, FSTRANS_NORMAL); default: return EINVAL; } } This is an example of a file system operation. int xxx_create(void *v) { struct vop_create_args *ap = v; struct mount *mp = ap->a_dvp->v_mount; int error; if ((error = fstrans_start(mp, FSTRANS_SHARED)) != 0) return error; /* Actually create the node. */ fstrans_done(mp); return 0; }
SEE ALSO
vfs_resume(9), vfs_suspend(9)
CODE REFERENCES
The actual code implementing this subsystem can be found in the file sys/kern/vfs_trans.c.
HISTORY
The fstrans subsystem appeared in NetBSD 5.0.
AUTHORS
The fstrans subsystem was written by Juergen Hannken-Illjes <hannken@NetBSD.org>. NetBSD 5.0 December 2, 2007 NetBSD 5.0
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