'\" t
.\"     Title: vfs_lock_file
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: September 2017
.\"    Manual: The Linux VFS
.\"    Source: Kernel Hackers Manual 4.12.13
.\"  Language: English
.\"
.TH "VFS_LOCK_FILE" "9" "September 2017" "Kernel Hackers Manual 4\&.12\&" "The Linux VFS"
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.SH "NAME"
vfs_lock_file \- file byte range lock
.SH "SYNOPSIS"
.HP \w'int\ vfs_lock_file('u
.BI "int vfs_lock_file(struct\ file\ *\ " "filp" ", unsigned\ int\ " "cmd" ", struct\ file_lock\ *\ " "fl" ", struct\ file_lock\ *\ " "conf" ");"
.SH "ARGUMENTS"
.PP
\fIstruct file * filp\fR
.RS 4
The file to apply the lock to
.RE
.PP
\fIunsigned int cmd\fR
.RS 4
type of locking operation (F_SETLK, F_GETLK, etc\&.)
.RE
.PP
\fIstruct file_lock * fl\fR
.RS 4
The lock to be applied
.RE
.PP
\fIstruct file_lock * conf\fR
.RS 4
Place to return a copy of the conflicting lock, if found\&.
.RE
.SH "DESCRIPTION"
.PP
A caller that doesn\*(Aqt care about the conflicting lock may pass NULL as the final argument\&.
.PP
If the filesystem defines a private \->\fBlock\fR
method, then
\fIconf\fR
will be left unchanged; so a caller that cares should initialize it to some acceptable default\&.
.PP
To avoid blocking kernel daemons, such as lockd, that need to acquire POSIX locks, the \->\fBlock\fR
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 \->\fBlock\fR
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 \->\fBlock\fR
does return asynchronously, it must return FILE_LOCK_DEFERRED, and call \->\fBlm_grant\fR
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 \->\fBlm_grant\fR
before returning to the caller with a FILE_LOCK_DEFERRED return code\&.
.SH "COPYRIGHT"
.br