user_namespaces.7: Minor rewordings of recently added text

[thirdparty/man-pages.git] / man3 / fts.3

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.\"     @(#)fts.3	8.5 (Berkeley) 4/16/94
.\"
.\" 2007-12-08, mtk, Converted from mdoc to man macros
.\"
.TH FTS 3 2018-02-02 "Linux" "Linux Programmer's Manual"
.SH NAME
fts, fts_open, fts_read, fts_children, fts_set, fts_close \- \
traverse a file hierarchy
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <sys/stat.h>
.B #include <fts.h>
.PP
.BI "FTS *fts_open(char * const *" path_argv ", int " options ", "
.BI "              int (*" compar ")(const FTSENT **, const FTSENT **));"
.PP
.BI "FTSENT *fts_read(FTS *" ftsp );
.PP
.BI "FTSENT *fts_children(FTS *" ftsp ", int " instr );
.PP
.BI "int fts_set(FTS *" ftsp ", FTSENT *" f ", int " instr );
.PP
.BI "int fts_close(FTS *" ftsp );
.fi
.SH DESCRIPTION
The
fts functions are provided for traversing
file hierarchies.
A simple overview is that the
.BR fts_open ()
function returns a "handle" (of type
.IR "FTS\ *" )
that refers to a file hierarchy "stream".
This handle is then supplied to the other
fts functions.
The function
.BR fts_read ()
returns a pointer to a structure describing one of the files in the file
hierarchy.
The function
.BR fts_children ()
returns a pointer to a linked list of structures, each of which describes
one of the files contained in a directory in the hierarchy.
.PP
In general, directories are visited two distinguishable times; in preorder
(before any of their descendants are visited) and in postorder (after all
of their descendants have been visited).
Files are visited once.
It is possible to walk the hierarchy "logically" (visiting the files that
symbolic links point to)
or physically (visiting the symbolic links themselves),
order the walk of the hierarchy or
prune and/or revisit portions of the hierarchy.
.PP
Two structures (and associated types) are defined in the include file
.IR <fts.h> .
The first type is
.IR FTS ,
the structure that represents the file hierarchy itself.
The second type is
.IR FTSENT ,
the structure that represents a file in the file
hierarchy.
Normally, an
.I FTSENT
structure is returned for every file in the file
hierarchy.
In this manual page, "file" and
"FTSENT structure"
are generally interchangeable.
.PP
The
.I FTSENT
structure contains fields describing a file.
The structure contains at least the following fields
(there are additional fields that
should be considered private to the implementation):
.PP
.in +4n
.EX
typedef struct _ftsent {
    unsigned short  fts_info;     /* flags for FTSENT structure */
    char           *fts_accpath;  /* access path */
    char           *fts_path;     /* root path */
    short           fts_pathlen;  /* strlen(fts_path) +
                                     strlen(fts_name) */
    char           *fts_name;     /* filename */
    short           fts_namelen;  /* strlen(fts_name) */
    short           fts_level;    /* depth (\-1 to N) */
    int             fts_errno;    /* file errno */
    long            fts_number;   /* local numeric value */
    void           *fts_pointer;  /* local address value */
    struct _ftsent *fts_parent;   /* parent directory */
    struct _ftsent *fts_link;     /* next file structure */
    struct _ftsent *fts_cycle;    /* cycle structure */
    struct stat    *fts_statp;    /* stat(2) information */
.\" Also:
.\"     ino_t fts_ino;                  /* inode (only for directories)*/
.\"     dev_t fts_dev;                  /* device (only for directories)*/
.\"     nlink_t fts_nlink;              /* link count (only for directories)*/
.\"     u_short fts_flags;              /* private flags for FTSENT structure */
.\"     u_short fts_instr;              /* fts_set() instructions */
} FTSENT;
.EE
.in
.PP
These fields are defined as follows:
.\" .Bl -tag -width "fts_namelen"
.TP 12
.IR fts_info
One of the following values describing the returned
.I FTSENT
structure and
the file it represents.
With the exception of directories without errors
.RB ( FTS_D ),
all of these
entries are terminal, that is, they will not be revisited, nor will any
of their descendants be visited.
.\" .Bl  -tag -width FTS_DEFAULT
.RS 12
.TP 12
.BR FTS_D
A directory being visited in preorder.
.TP
.BR FTS_DC
A directory that causes a cycle in the tree.
(The
.I fts_cycle
field of the
.I FTSENT
structure will be filled in as well.)
.TP
.BR FTS_DEFAULT
Any
.I FTSENT
structure that represents a file type not explicitly described
by one of the other
.I fts_info
values.
.TP
.BR FTS_DNR
A directory which cannot be read.
This is an error return, and the
.I fts_errno
field will be set to indicate what caused the error.
.TP
.BR FTS_DOT
A file named
"."
or
".."
which was not specified as a filename to
.BR fts_open ()
(see
.BR FTS_SEEDOT ).
.TP
.BR FTS_DP
A directory being visited in postorder.
The contents of the
.I FTSENT
structure will be unchanged from when
it was returned in preorder, that is, with the
.I fts_info
field set to
.BR FTS_D .
.TP
.BR FTS_ERR
This is an error return, and the
.I fts_errno
field will be set to indicate what caused the error.
.TP
.BR FTS_F
A regular file.
.TP
.BR FTS_NS
A file for which no
.BR stat (2)
information was available.
The contents of the
.I fts_statp
field are undefined.
This is an error return, and the
.I fts_errno
field will be set to indicate what caused the error.
.TP
.BR FTS_NSOK
A file for which no
.BR stat (2)
information was requested.
The contents of the
.I fts_statp
field are undefined.
.TP
.BR FTS_SL
A symbolic link.
.TP
.BR FTS_SLNONE
A symbolic link with a nonexistent target.
The contents of the
.I fts_statp
field reference the file characteristic information for the symbolic link
itself.
.\" .El
.RE
.TP
.IR fts_accpath
A path for accessing the file from the current directory.
.TP
.IR fts_path
The path for the file relative to the root of the traversal.
This path contains the path specified to
.BR fts_open ()
as a prefix.
.TP
.IR fts_pathlen
The sum of the lengths of the strings referenced by
.IR fts_path
and
.IR fts_name .
.TP
.IR fts_name
The name of the file.
.TP
.IR fts_namelen
The length of the string referenced by
.IR fts_name .
.TP
.IR fts_level
The depth of the traversal, numbered from \-1 to N, where this file
was found.
The
.I FTSENT
structure representing the parent of the starting point (or root)
of the traversal is numbered \-1, and the
.I FTSENT
structure for the root
itself is numbered 0.
.TP
.IR fts_errno
If
.BR fts_children ()
or
.BR fts_read ()
returns an
.I FTSENT
structure whose
.I fts_info
field is set to
.BR FTS_DNR ,
.BR FTS_ERR ,
or
.BR FTS_NS ,
the
.I fts_errno
field contains the error number (i.e., the
.IR errno
value)
specifying the cause of the error.
Otherwise, the contents of the
.I fts_errno
field are undefined.
.TP
.IR fts_number
This field is provided for the use of the application program and is
not modified by the
fts functions.
It is initialized to 0.
.TP
.IR fts_pointer
This field is provided for the use of the application program and is
not modified by the
fts functions.
It is initialized to
NULL.
.TP
.IR fts_parent
A pointer to the
.I FTSENT
structure referencing the file in the hierarchy
immediately above the current file, that is, the directory of which this
file is a member.
A parent structure for the initial entry point is provided as well,
however, only the
.IR fts_level ,
.IR fts_number ,
and
.I fts_pointer
fields are guaranteed to be initialized.
.TP
.IR fts_link
Upon return from the
.BR fts_children ()
function, the
.I fts_link
field points to the next structure in the NULL-terminated linked list of
directory members.
Otherwise, the contents of the
.I fts_link
field are undefined.
.TP
.IR fts_cycle
If a directory causes a cycle in the hierarchy (see
.BR FTS_DC ),
either because
of a hard link between two directories, or a symbolic link pointing to a
directory, the
.I fts_cycle
field of the structure will point to the
.I FTSENT
structure in the hierarchy that references the same file as the current
.I FTSENT
structure.
Otherwise, the contents of the
.I fts_cycle
field are undefined.
.TP
.IR fts_statp
A pointer to
.BR stat (2)
information for the file.
.\" .El
.PP
A single buffer is used for all of the paths of all of the files in the
file hierarchy.
Therefore, the
.I fts_path
and
.I fts_accpath
fields are guaranteed to be
null-terminated
.I only
for the file most recently returned by
.BR fts_read ().
To use these fields to reference any files represented by other
.I FTSENT
structures will require that the path buffer be modified using the
information contained in that
.I FTSENT
structure's
.I fts_pathlen
field.
Any such modifications should be undone before further calls to
.BR fts_read ()
are attempted.
The
.I fts_name
field is always
null-terminated.
.SS fts_open()
The
.BR fts_open ()
function takes a pointer to an array of character pointers naming one
or more paths which make up a logical file hierarchy to be traversed.
The array must be terminated by a
null pointer.
.PP
There are
a number of options, at least one of which (either
.BR FTS_LOGICAL
or
.BR FTS_PHYSICAL )
must be specified.
The options are selected by ORing
the following values:
.\" .Bl -tag -width "FTS_PHYSICAL"
.TP 14
.BR FTS_COMFOLLOW
This option causes any symbolic link specified as a root path to be
followed immediately whether or not
.BR FTS_LOGICAL
is also specified.
.TP
.BR FTS_LOGICAL
This option causes the
fts routines to return
.I FTSENT
structures for the targets of symbolic links
instead of the symbolic links themselves.
If this option is set, the only symbolic links for which
.I FTSENT
structures
are returned to the application are those referencing nonexistent files.
Either
.BR FTS_LOGICAL
or
.BR FTS_PHYSICAL
.I must
be provided to the
.BR fts_open ()
function.
.TP
.BR FTS_NOCHDIR
As a performance optimization, the
fts functions change directories as they walk the file hierarchy.
This has the side-effect that an application cannot rely on being
in any particular directory during the traversal.
The
.BR FTS_NOCHDIR
option turns off this optimization, and the
fts functions will not change the current directory.
Note that applications should not themselves change their current directory
and try to access files unless
.BR FTS_NOCHDIR
is specified and absolute
pathnames were provided as arguments to
.BR fts_open ().
.TP
.BR FTS_NOSTAT
By default, returned
.I FTSENT
structures reference file characteristic information (the
.I statp
field) for each file visited.
This option relaxes that requirement as a performance optimization,
allowing the
fts functions to set the
.I fts_info
field to
.BR FTS_NSOK
and leave the contents of the
.I statp
field undefined.
.TP
.BR FTS_PHYSICAL
This option causes the
fts routines to return
.I FTSENT
structures for symbolic links themselves instead
of the target files they point to.
If this option is set,
.I FTSENT
structures for all symbolic links in the
hierarchy are returned to the application.
Either
.BR FTS_LOGICAL
or
.BR FTS_PHYSICAL
.I must
be provided to the
.BR fts_open ()
function.
.TP
.BR FTS_SEEDOT
By default, unless they are specified as path arguments to
.BR fts_open (),
any files named
"."
or
".."
encountered in the file hierarchy are ignored.
This option causes the
fts routines to return
.I FTSENT
structures for them.
.TP
.BR FTS_XDEV
This option prevents
fts from descending into directories that have a different device number
than the file from which the descent began.
.\" .El
.PP
The argument
.BR compar ()
specifies a user-defined function which may be used to order the traversal
of the hierarchy.
It
takes two pointers to pointers to
.I FTSENT
structures as arguments and
should return a negative value, zero, or a positive value to indicate
if the file referenced by its first argument comes before, in any order
with respect to, or after, the file referenced by its second argument.
The
.IR fts_accpath ,
.IR fts_path ,
and
.I fts_pathlen
fields of the
.I FTSENT
structures may
.I never
be used in this comparison.
If the
.I fts_info
field is set to
.BR FTS_NS
or
.BR FTS_NSOK ,
the
.I fts_statp
field may not either.
If the
.BR compar ()
argument is
NULL,
the directory traversal order is in the order listed in
.I path_argv
for the root paths, and in the order listed in the directory for
everything else.
.SS fts_read()
The
.BR fts_read ()
function returns a pointer to an
.I FTSENT
structure describing a file in
the hierarchy.
Directories (that are readable and do not cause cycles) are visited at
least twice, once in preorder and once in postorder.
All other files are visited at least once.
(Hard links between directories that do not cause cycles or symbolic
links to symbolic links may cause files to be visited more than once,
or directories more than twice.)
.PP
If all the members of the hierarchy have been returned,
.BR fts_read ()
returns
NULL
and sets the external variable
.I errno
to 0.
If an error unrelated to a file in the hierarchy occurs,
.BR fts_read ()
returns
NULL
and sets
.I errno
appropriately.
If an error related to a returned file occurs, a pointer to an
.I FTSENT
structure is returned, and
.I errno
may or may not have been set (see
.IR fts_info ).
.PP
The
.I FTSENT
structures returned by
.BR fts_read ()
may be overwritten after a call to
.BR fts_close ()
on the same file hierarchy stream, or, after a call to
.BR fts_read ()
on the same file hierarchy stream unless they represent a file of type
directory, in which case they will not be overwritten until after a call to
.BR fts_read ()
after the
.I FTSENT
structure has been returned by the function
.BR fts_read ()
in postorder.
.SS fts_children()
The
.BR fts_children ()
function returns a pointer to an
.I FTSENT
structure describing the first entry in a NULL-terminated linked list of
the files in the directory represented by the
.I FTSENT
structure most recently returned by
.BR fts_read ().
The list is linked through the
.I fts_link
field of the
.I FTSENT
structure, and is ordered by the user-specified comparison function, if any.
Repeated calls to
.BR fts_children ()
will re-create this linked list.
.PP
As a special case, if
.BR fts_read ()
has not yet been called for a hierarchy,
.BR fts_children ()
will return a pointer to the files in the logical directory specified to
.BR fts_open (),
that is, the arguments specified to
.BR fts_open ().
Otherwise, if the
.I FTSENT
structure most recently returned by
.BR fts_read ()
is not a directory being visited in preorder,
or the directory does not contain any files,
.BR fts_children ()
returns
NULL
and sets
.I errno
to zero.
If an error occurs,
.BR fts_children ()
returns
NULL
and sets
.I errno
appropriately.
.PP
The
.I FTSENT
structures returned by
.BR fts_children ()
may be overwritten after a call to
.BR fts_children (),
.BR fts_close (),
or
.BR fts_read ()
on the same file hierarchy stream.
.PP
The
.I instr
argument is either zero or the following value:
.\" .Bl -tag -width FTS_NAMEONLY
.TP 13
.BR FTS_NAMEONLY
Only the names of the files are needed.
The contents of all the fields in the returned linked list of structures
are undefined with the exception of the
.I fts_name
and
.I fts_namelen
fields.
.\" .El
.SS fts_set()
The function
.BR fts_set ()
allows the user application to determine further processing for the
file
.I f
of the stream
.IR ftsp .
The
.BR fts_set ()
function
returns 0 on success, and \-1 if an error occurs.
.PP
The
.I instr
argument is either 0 (meaning "do nothing") or one of the following values:
.\" .Bl -tag -width FTS_PHYSICAL
.TP 13
.BR FTS_AGAIN
Revisit the file; any file type may be revisited.
The next call to
.BR fts_read ()
will return the referenced file.
The
.I fts_stat
and
.I fts_info
fields of the structure will be reinitialized at that time,
but no other fields will have been changed.
This option is meaningful only for the most recently returned
file from
.BR fts_read ().
Normal use is for postorder directory visits, where it causes the
directory to be revisited (in both preorder and postorder) as well as all
of its descendants.
.TP
.BR FTS_FOLLOW
The referenced file must be a symbolic link.
If the referenced file is the one most recently returned by
.BR fts_read (),
the next call to
.BR fts_read ()
returns the file with the
.I fts_info
and
.I fts_statp
fields reinitialized to reflect the target of the symbolic link instead
of the symbolic link itself.
If the file is one of those most recently returned by
.BR fts_children (),
the
.I fts_info
and
.I fts_statp
fields of the structure, when returned by
.BR fts_read (),
will reflect the target of the symbolic link instead of the symbolic link
itself.
In either case, if the target of the symbolic link does not exist, the
fields of the returned structure will be unchanged and the
.I fts_info
field will be set to
.BR FTS_SLNONE .
.IP
If the target of the link is a directory, the preorder return, followed
by the return of all of its descendants, followed by a postorder return,
is done.
.TP
.BR FTS_SKIP
No descendants of this file are visited.
The file may be one of those most recently returned by either
.BR fts_children ()
or
.BR fts_read ().
.\" .El
.SS fts_close()
The
.BR fts_close ()
function closes the file hierarchy stream referred to by
.I ftsp
and restores the current directory to the directory from which
.BR fts_open ()
was called to open
.IR ftsp .
The
.BR fts_close ()
function
returns 0 on success, and \-1 if an error occurs.
.SH ERRORS
The function
.BR fts_open ()
may fail and set
.I errno
for any of the errors specified for
.BR open (2)
and
.BR malloc (3).
.PP
The function
.BR fts_close ()
may fail and set
.I errno
for any of the errors specified for
.BR chdir (2)
and
.BR close (2).
.PP
The functions
.BR fts_read ()
and
.BR fts_children ()
may fail and set
.I errno
for any of the errors specified for
.BR chdir (2),
.BR malloc (3),
.BR opendir (3),
.BR readdir (3),
and
.BR stat (2).
.PP
In addition,
.BR fts_children (),
.BR fts_open (),
and
.BR fts_set ()
may fail and set
.I errno
as follows:
.TP
.B EINVAL
.I options
or
.I instr
was invalid.
.SH VERSIONS
These functions are available in Linux since glibc2.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbw34 lb lb
l l l.
Interface	Attribute	Value
T{
.BR fts_open (),
.BR fts_set (),
.BR fts_close ()
T}	Thread safety	MT-Safe
T{
.BR fts_read (),
.BR fts_children ()
T}	Thread safety	MT-Unsafe
.TE
.sp 1
.SH CONFORMING TO
4.4BSD.
.SH BUGS
In versions of glibc before 2.23,
.\" Fixed by commit 8b7b7f75d91f7bac323dd6a370aeb3e9c5c4a7d5
.\" https://sourceware.org/bugzilla/show_bug.cgi?id=15838
.\" https://sourceware.org/bugzilla/show_bug.cgi?id=11460
all of the APIs described in this man page are not safe when compiling
a program using the LFS APIs (e.g., when compiling with
.IR -D_FILE_OFFSET_BITS=64 ).
.\"
.\" The following statement is years old, and seems no closer to
.\" being true -- mtk
.\" The
.\" .I fts
.\" utility is expected to be included in a future
.\" POSIX.1
.\" revision.
.SH SEE ALSO
.BR find (1),
.BR chdir (2),
.BR stat (2),
.BR ftw (3),
.BR qsort (3)