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Added discussion of resolved_path == NULL

This commit is contained in:
Michael Kerrisk 2004-12-15 15:18:55 +00:00
parent 5d6d14a0c4
commit 7841ad4741
1 changed files with 29 additions and 7 deletions
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36
man3/realpath.3
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@ -21,8 +21,9 @@
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" Rewritten old page, 990824, aeb@cwi.nl
.\" 2004-12-14, mtk, added discussion of resolved_path == NULL
.\"
.TH REALPATH 3 1999-08-24 "" "Linux Programmer's Manual"
.TH REALPATH 3 2004-12-14 "" "Linux Programmer's Manual"
.SH NAME
realpath \- return the canonicalized absolute pathname
.SH SYNOPSIS
@ -32,7 +33,7 @@ realpath \- return the canonicalized absolute pathname
.sp
.BI "char *realpath(const char *" path ", char *" resolved_path );
.SH DESCRIPTION
.B realpath
.BR realpath ()
expands all symbolic links and resolves references
to
.IR '/./' ", " '/../'
@ -50,7 +51,9 @@ or
.I '/../'
components.
.SH "RETURN VALUE"
If there is no error, it returns a pointer to the
If there is no error,
.BR realpath ()
returns a pointer to the
.IR resolved_path .
Otherwise it returns a NULL pointer, and the contents
@ -70,6 +73,7 @@ Either
or
.I resolved_path
is NULL. (In libc5 this would just cause a segfault.)
But, see NOTES below.
.TP
.B EIO
An I/O error occurred while reading from the file system.
@ -89,9 +93,27 @@ The named file does not exist.
.TP
.B ENOTDIR
A component of the path prefix is not a directory.
.SH NOTES
The glibc implementation of
.BR realpath ()
provides a non-standard extension.
If
.I resolved_path
is specified as NULL, then
.BR realpath ()
uses
.BR malloc (3)
to allocate a buffer to hold the resolved pathname,
and returns a pointer to this buffer.
The caller should deallocate this buffer using
.BR free (3).
.\" FIXME? In my testing, even if we use resolved_path == NULL, then
.\" realpath() will still return ENAMETOOLONG if the resolved pathname
.\" would exceed PATH_MAX bytes -- MTK, Dec 04
.SH BUGS
Never use this function. It is broken by design since it is
impossible to determine a suitable size for the output buffer.
Avoiid using this function. It is broken by design since it is
impossible to determine a suitable size for the output buffer,
.IR resolved_path .
According to POSIX a buffer of size PATH_MAX suffices, but
PATH_MAX need not be a defined constant, and may have to be
obtained using
@ -111,7 +133,7 @@ The libc4 and libc5 implementation contains a buffer overflow
Thus, suid programs like mount need a private version.
.SH HISTORY
The
.B realpath
.BR realpath ()
function first appeared in BSD 4.4, contributed by Jan-Simon Pendry.
In Linux this function appears in libc 4.5.21.
.SH "CONFORMING TO"
@ -139,7 +161,7 @@ path name. Solaris may return a relative path name when the
.I path
argument is relative.
The prototype of
.B realpath
.BR realpath ()
is given in <unistd.h> in libc4 and libc5,
but in <stdlib.h> everywhere else.
.SH "SEE ALSO"