freebsd-src/lib/libsys/readlink.2

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.Dd March 30, 2020
.Dt READLINK 2
.Os
.Sh NAME
.Nm readlink ,
.Nm readlinkat
.Nd read value of a symbolic link
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft ssize_t
.Fn readlink "const char *restrict path" "char *restrict buf" "size_t bufsiz"
.Ft ssize_t
.Fo readlinkat
.Fa "int fd" "const char *restrict path" "char *restrict buf" "size_t bufsize"
.Fc
.Sh DESCRIPTION
The
.Fn readlink
system call
places the contents of the symbolic link
.Fa path
in the buffer
.Fa buf ,
which has size
.Fa bufsiz .
The
.Fn readlink
system call does not append a
.Dv NUL
character to
.Fa buf .
.Pp
The
.Fn readlinkat
system call is equivalent to
.Fn readlink
except in the case where
.Fa path
specifies a relative path.
In this case the symbolic link whose content is read relative to the
directory associated with the file descriptor
.Fa fd
instead of the current working directory.
If
.Fn readlinkat
is passed the special value
.Dv AT_FDCWD
in the
.Fa fd
parameter, the current working directory is used and the behavior is
identical to a call to
.Fn readlink .
.Sh RETURN VALUES
The call returns the count of characters placed in the buffer
if it succeeds, or a \-1 if an error occurs, placing the error
code in the global variable
.Va errno .
.Sh ERRORS
The
.Fn readlink
system call
will fail if:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
.It Bq Er ENOENT
The named file does not exist.
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EINVAL
The named file is not a symbolic link.
.It Bq Er EIO
An I/O error occurred while reading from the file system.
.It Bq Er EINTEGRITY
Corrupted data was detected while reading from the file system.
.It Bq Er EFAULT
The
.Fa buf
argument
extends outside the process's allocated address space.
.El
.Pp
In addition to the errors returned by the
.Fn readlink ,
the
.Fn readlinkat
may fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa path
argument does not specify an absolute path and the
.Fa fd
argument is neither
.Dv AT_FDCWD
nor a valid file descriptor open for searching.
.It Bq Er ENOTDIR
The
.Fa path
argument is not an absolute path and
.Fa fd
is neither
.Dv AT_FDCWD
nor a file descriptor associated with a directory.
.El
.Sh SEE ALSO
.Xr lstat 2 ,
.Xr stat 2 ,
.Xr symlink 2 ,
.Xr symlink 7
.Sh STANDARDS
The
.Fn readlinkat
system call follows The Open Group Extended API Set 2 specification.
.Sh HISTORY
The
.Fn readlink
system call appeared in
.Bx 4.2 .
The
.Fn readlinkat
system call appeared in
.Fx 8.0 .