path: root/man3/fpathconf.3

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.\" FIXME Probably all of the following should be documented:
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.\"     _PC_ASYNC_IO,
.\"     _PC_PRIO_IO,
.\"     _PC_SOCK_MAXBUF,
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.TH fpathconf 3 2023-10-31 "Linux man-pages 6.7"
.SH NAME
fpathconf, pathconf \- get configuration values for files
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <unistd.h>
.P
.BI "long fpathconf(int " fd ", int " name );
.BI "long pathconf(const char *" path ", int " name );
.fi
.SH DESCRIPTION
.BR fpathconf ()
gets a value for the configuration option
.I name
for the open file descriptor
.IR fd .
.P
.BR pathconf ()
gets a value for configuration option
.I name
for the filename
.IR path .
.P
The corresponding macros defined in
.I <unistd.h>
are minimum values; if an application wants to take advantage of values
which may change, a call to
.BR fpathconf ()
or
.BR pathconf ()
can be made, which may yield more liberal results.
.P
Setting
.I name
equal to one of the following constants returns the following
configuration options:
.TP
.B _PC_LINK_MAX
The maximum number of links to the file.
If
.I fd
or
.I path
refer to a directory, then the value applies to the whole directory.
The corresponding macro is
.BR _POSIX_LINK_MAX .
.TP
.B _PC_MAX_CANON
The maximum length of a formatted input line, where
.I fd
or
.I path
must refer to a terminal.
The corresponding macro is
.BR _POSIX_MAX_CANON .
.TP
.B _PC_MAX_INPUT
The maximum length of an input line, where
.I fd
or
.I path
must refer to a terminal.
The corresponding macro is
.BR _POSIX_MAX_INPUT .
.TP
.B _PC_NAME_MAX
The maximum length of a filename in the directory
.I path
or
.I fd
that the process is allowed to create.
The corresponding macro is
.BR _POSIX_NAME_MAX .
.TP
.B _PC_PATH_MAX
The maximum length of a relative pathname when
.I path
or
.I fd
is the current working directory.
The corresponding macro is
.BR _POSIX_PATH_MAX .
.TP
.B _PC_PIPE_BUF
The maximum number of bytes that can be written atomically to a pipe of FIFO.
For
.BR fpathconf (),
.I fd
should refer to a pipe or FIFO.
For
.BR fpathconf (),
.I path
should refer to a FIFO or a directory; in the latter case,
the returned value corresponds to FIFOs created in that directory.
The corresponding macro is
.BR _POSIX_PIPE_BUF .
.TP
.B _PC_CHOWN_RESTRICTED
This returns a positive value if the use of
.BR chown (2)
and
.BR fchown (2)
for changing a file's user ID is restricted to a process
with appropriate privileges,
and changing a file's group ID to a value other than the process's
effective group ID or one of its supplementary group IDs
is restricted to a process with appropriate privileges.
According to POSIX.1,
this variable shall always be defined with a value other than \-1.
The corresponding macro is
.BR _POSIX_CHOWN_RESTRICTED .
.IP
If
.I fd
or
.I path
refers to a directory,
then the return value applies to all files in that directory.
.TP
.B _PC_NO_TRUNC
This returns nonzero if accessing filenames longer than
.B _POSIX_NAME_MAX
generates an error.
The corresponding macro is
.BR _POSIX_NO_TRUNC .
.TP
.B _PC_VDISABLE
This returns nonzero if special character processing can be disabled, where
.I fd
or
.I path
must refer to a terminal.
.SH RETURN VALUE
The return value of these functions is one of the following:
.IP \[bu] 3
On error, \-1 is returned and
.I errno
is set to indicate the error
(for example,
.BR EINVAL ,
indicating that
.I name
is invalid).
.IP \[bu]
If
.I name
corresponds to a maximum or minimum limit, and that limit is indeterminate,
\-1 is returned and
.I errno
is not changed.
(To distinguish an indeterminate limit from an error, set
.I errno
to zero before the call, and then check whether
.I errno
is nonzero when \-1 is returned.)
.IP \[bu]
If
.I name
corresponds to an option,
a positive value is returned if the option is supported,
and \-1 is returned if the option is not supported.
.IP \[bu]
Otherwise,
the current value of the option or limit is returned.
This value will not be more restrictive than
the corresponding value that was described to the application in
.I <unistd.h>
or
.I <limits.h>
when the application was compiled.
.SH ERRORS
.TP
.B EACCES
.RB ( pathconf ())
Search permission is denied for one of the directories in the path prefix of
.IR path .
.TP
.B EBADF
.RB ( fpathconf ())
.I fd
is not a valid file descriptor.
.TP
.B EINVAL
.I name
is invalid.
.TP
.B EINVAL
The implementation does not support an association of
.I name
with the specified file.
.TP
.B ELOOP
.RB ( pathconf ())
Too many symbolic links were encountered while resolving
.IR path .
.TP
.B ENAMETOOLONG
.RB ( pathconf ())
.I path
is too long.
.TP
.B ENOENT
.RB ( pathconf ())
A component of
.I path
does not exist, or
.I path
is an empty string.
.TP
.B ENOTDIR
.RB ( pathconf ())
A component used as a directory in
.I path
is not in fact a directory.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR fpathconf (),
.BR pathconf ()
T}	Thread safety	MT-Safe
.TE
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
POSIX.1-2001.
.SH NOTES
Files with name lengths longer than the value returned for
.I name
equal to
.B _PC_NAME_MAX
may exist in the given directory.
.P
Some returned values may be huge; they are not suitable for allocating
memory.
.SH SEE ALSO
.BR getconf (1),
.BR open (2),
.BR statfs (2),
.BR confstr (3),
.BR sysconf (3)