'\" t
.\"     Title: vfs_rename
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: July 2017
.\"    Manual: The Linux VFS
.\"    Source: Kernel Hackers Manual 4.12.2
.\"  Language: English
.\"
.TH "VFS_RENAME" "9" "July 2017" "Kernel Hackers Manual 4\&.12\&" "The Linux VFS"
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.SH "NAME"
vfs_rename \- rename a filesystem object
.SH "SYNOPSIS"
.HP \w'int\ vfs_rename('u
.BI "int vfs_rename(struct\ inode\ *\ " "old_dir" ", struct\ dentry\ *\ " "old_dentry" ", struct\ inode\ *\ " "new_dir" ", struct\ dentry\ *\ " "new_dentry" ", struct\ inode\ **\ " "delegated_inode" ", unsigned\ int\ " "flags" ");"
.SH "ARGUMENTS"
.PP
\fIstruct inode * old_dir\fR
.RS 4
parent of source
.RE
.PP
\fIstruct dentry * old_dentry\fR
.RS 4
source
.RE
.PP
\fIstruct inode * new_dir\fR
.RS 4
parent of destination
.RE
.PP
\fIstruct dentry * new_dentry\fR
.RS 4
destination
.RE
.PP
\fIstruct inode ** delegated_inode\fR
.RS 4
returns an inode needing a delegation break
.RE
.PP
\fIunsigned int flags\fR
.RS 4
rename flags
.RE
.SH "DESCRIPTION"
.PP
The caller must hold multiple mutexes\-\-see
\fBlock_rename\fR)\&.
.PP
If vfs_rename discovers a delegation in need of breaking at either the source or destination, it will return \-EWOULDBLOCK and return a reference to the inode in delegated_inode\&. The caller should then break the delegation and retry\&. Because breaking a delegation may take a long time, the caller should drop all locks before doing so\&.
.PP
Alternatively, a caller may pass NULL for delegated_inode\&. This may be appropriate for callers that expect the underlying filesystem not to be NFS exported\&.
.PP
The worst of all namespace operations \- renaming directory\&.
\(lqPerverted\(rq
doesn\*(Aqt even start to describe it\&. Somebody in UCB had a heck of a trip\&.\&.\&. Problems: a) we can get into loop creation\&. b) race potential \- two innocent renames can create a loop together\&. That\*(Aqs where 4\&.4 screws up\&. Current fix: serialization on sb\->s_vfs_rename_mutex\&. We might be more accurate, but that\*(Aqs another story\&. c) we have to lock _four_ objects \- parents and victim (if it exists), and source (if it is not a directory)\&. And that \- after we got \->i_mutex on parents (until then we don\*(Aqt know whether the target exists)\&. Solution: try to be smart with locking order for inodes\&. We rely on the fact that tree topology may change only under \->s_vfs_rename_mutex _and_ that parent of the object we move will be locked\&. Thus we can rank directories by the tree (ancestors first) and rank all non\-directories after them\&. That works since everybody except rename does
\(lqlock parent, lookup, lock child\(rq
and rename is under \->s_vfs_rename_mutex\&. HOWEVER, it relies on the assumption that any object with \->\fBlookup\fR
has no more than 1 dentry\&. If
\(lqhybrid\(rq
objects will ever appear, we\*(Aqd better make sure that there\*(Aqs no link(2) for them\&. d) conversion from fhandle to dentry may come in the wrong moment \- when we are removing the target\&. Solution: we will have to grab \->i_mutex in the fhandle_to_dentry code\&. [FIXME \- current nfsfh\&.c relies on \->i_mutex on parents, which works but leads to some truly excessive locking]\&.
.SH "COPYRIGHT"
.br