vfs_lock_file(9) [centos man page]

VFS_LOCK_FILE(9)						   The Linux VFS						  VFS_LOCK_FILE(9)

NAME

       vfs_lock_file - file byte range lock

SYNOPSIS

       int vfs_lock_file(struct file * filp, unsigned int cmd, struct file_lock * fl, struct file_lock * conf);

ARGUMENTS

       filp
	   The file to apply the lock to

       cmd
	   type of locking operation (F_SETLK, F_GETLK, etc.)

       fl
	   The lock to be applied

       conf
	   Place to return a copy of the conflicting lock, if found.

DESCRIPTION

       A caller that doesn't care about the conflicting lock may pass NULL as the final argument.

       If the filesystem defines a private ->lock method, then conf will be left unchanged; so a caller that cares should initialize it to some
       acceptable default.

       To avoid blocking kernel daemons, such as lockd, that need to acquire POSIX locks, the ->lock interface may return asynchronously, before
       the lock has been granted or denied by the underlying filesystem, if (and only if) lm_grant is set. Callers expecting ->lock to return
       asynchronously will only use F_SETLK, not F_SETLKW; they will set FL_SLEEP if (and only if) the request is for a blocking lock. When ->lock
       does return asynchronously, it must return FILE_LOCK_DEFERRED, and call ->lm_grant when the lock request completes. If the request is for
       non-blocking lock the file system should return FILE_LOCK_DEFERRED then try to get the lock and call the callback routine with the result.
       If the request timed out the callback routine will return a nonzero return code and the file system should release the lock. The file
       system is also responsible to keep a corresponding posix lock when it grants a lock so the VFS can find out which locks are locally held
       and do the correct lock cleanup when required. The underlying filesystem must not drop the kernel lock or call ->lm_grant before returning
       to the caller with a FILE_LOCK_DEFERRED return code.

COPYRIGHT

Kernel Hackers Manual 3.10					     June 2014							  VFS_LOCK_FILE(9)

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lock_try_read(9r)														 lock_try_read(9r)

NAME

       lock_try_read - General: Tries to assert a complex lock with read-only access

SYNOPSIS

       #include <kern/lock.h>

       boolean_t lock_try_read(
	       lock_t lock_structptr );

ARGUMENTS

       Specifies  a  pointer to the complex lock structure, lock. This is the lock structure associated with the resource on which you want to try
       to assert a complex lock with read-only access. The lock structure is an opaque data structure; that is, its associated members are  refer-
       enced and manipulated by the operating system and not by the user of the complex lock mechanism.

DESCRIPTION

       The  lock_try_read  routine  tries  to  assert a complex lock (without blocking) with read-only access for the resource associated with the
       specified lock structure pointer. To release a complex lock  with  read-only  access  successfully  asserted  by  lock_try_read,  call  the
       lock_done routine.

NOTES

       You  must call lock_init (once only) prior to calling lock_try_read to initialize the lock structure pointer for the resource.  A resource,
       from the kernel module's standpoint, is data that more than one kernel thread can manipulate. You can store the resource  in  global  vari-
       ables and in data structure members.

RETURN VALUES

       The  lock_try_read  routine  returns  one  of  the following values: The attempt to acquire the read-only complex lock was successful.  The
       attempt to acquire the read-only complex lock was unsuccessful.

FILES

SEE ALSO

       Routines: lock_done(9r), lock_terminate(9r), lock_try_write(9r), lock_write(9r)

       Data Structures: lock(9s)

																 lock_try_read(9r)

Linux and UNIX Man Pages

vfs_lock_file(9) [centos man page]

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