[PATCH] lib/cmd/bup.c: Accomodate historical realpath

[Greg Troxel]

realpath(3) originally required a non-NULL 2nd argument. POSIX
extended it to allow NULL, but some old BSD versions still have the
as-first-introduced-in-4.4BSD implementation that does not accept the
2nd argument being NULL.

Define bup_realpath, which collapses to just system realpath for most
systems, and on systems known to have historic realpath, use a buffer,
and strdup the results, to match the POSIX-with-NULL semantics.

Currently the alternate is used on all OpenBSD, pending contribution
of an appropriate preprocessor conditional. It also remains to
determine versions and write a conditional for Solaris.
---
lib/cmd/bup.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 47 insertions(+), 3 deletions(-)

diff --git a/lib/cmd/bup.c b/lib/cmd/bup.c
index 9cd1f38..ded7c5b 100644
--- a/lib/cmd/bup.c
+++ b/lib/cmd/bup.c
@@ -96,6 +96,50 @@ setup_bup_main_module(void) {
die(2, "unable to register bup_main module\n");
}

+/*
+ * The code below depends on realpath(3). The historical
+ * implementation in 4.4BSD required the second argument to be
+ * non-NULL, and POSIX added the option of NULL with the semantics of
+ * malloc'ing a big-enough buffer. We define a helper function with
+ * the NULL semantics to accomodate historical implementations.
+ *
+ * gnulib has a list of systems that are known to reject NULL as the
+ * 2nd argument:
+ * https://www.gnu.org/software/gnulib/manual/html_node/realpath.html
+ */
+/* FreeBSD < 7: bup's FreeBSD code does not use realpath(3) */
+#if defined(__NetBSD__) && !__NetBSD_Prereq__(7,0,0)
+#define OLD_REALPATH
+#endif
+#if defined(__OpenBSD__)
+/*
+ * This should only apply to versions < 5, but from reading
+ * src/param.h it is not clear how to write a preprocessor test.
+ */
+#define OLD_REALPATH
+#endif
+/* \todo Solaris 10; later versions unclear */
+
+char *
+bup_realpath(const char *pathname)
+{
+#ifndef OLD_REALPATH
+ return realpath(pathname, NULL);
+#else
+ char *ret;
+ char resolvedname[PATH_MAX];
+
+ ret = realpath(pathname, resolvedname);
+
+ if (ret != NULL)
+ {
+ assert(ret == resolvedname);
+ ret = strdup(ret);
+ }
+ return ret;
+#endif
+}
+
#if defined(__APPLE__) && defined(__MACH__)

static char *exe_parent_dir(const char * const argv_0) {
@@ -110,7 +154,7 @@ static char *exe_parent_dir(const char * const argv_0) {
}
if(rc != 0) die(2, "unable to find executable path\n");
char *path = mpath ? mpath : spath;
- char *abs_exe = realpath(path, NULL);
+ char *abs_exe = bup_realpath(path);
if (!abs_exe)
die(2, "cannot resolve path (%s): %s\n", strerror(errno), path);
char * const abs_parent = strdup(dirname(abs_exe));
@@ -215,7 +259,7 @@ static char *find_exe_parent(const char * const argv_0)
argv_0);
char *path_exe = find_in_path(argv_0, env_path);
if (path_exe) {
- char * abs_exe = realpath(path_exe, NULL);
+ char * abs_exe = bup_realpath(path_exe);
if (!abs_exe)
die(2, "cannot resolve path (%s): %s\n",
strerror(errno), path_exe);
@@ -226,7 +270,7 @@ static char *find_exe_parent(const char * const argv_0)
if (!candidate)
return NULL;

- char * const abs_exe = realpath(candidate, NULL);
+ char * const abs_exe = bup_realpath(candidate);
if (!abs_exe)
die(2, "cannot resolve path (%s): %s\n", strerror(errno), candidate);
free(candidate);
--
2.36.1

[Rob Browning]

Greg Troxel <g...@lexort.com> writes:

> Currently the alternate is used on all OpenBSD, pending contribution
> of an appropriate preprocessor conditional.

How about something like this?

#if defined(OpenBSD) && OpenBSD < 201111

via

https://cvsweb.openbsd.org/cgi-bin/cvsweb/src/sys/sys/param.h.diff?r1=1.91&r2=1.92&f=h

from:

https://cvsweb.openbsd.org/src/sys/sys/param.h

Thanks
--
Rob Browning
rlb @defaultvalue.org and @debian.org
GPG as of 2011-07-10 E6A9 DA3C C9FD 1FF8 C676 D2C4 C0F0 39E9 ED1B 597A
GPG as of 2002-11-03 14DD 432F AE39 534D B592 F9A0 25C8 D377 8C7E 73A4

[Rob Browning]

Greg Troxel <g...@lexort.com> writes:

> realpath(3) originally required a non-NULL 2nd argument. POSIX
> extended it to allow NULL, but some old BSD versions still have the
> as-first-introduced-in-4.4BSD implementation that does not accept the
> 2nd argument being NULL.
>
> Define bup_realpath, which collapses to just system realpath for most
> systems, and on systems known to have historic realpath, use a buffer,
> and strdup the results, to match the POSIX-with-NULL semantics.
>
> Currently the alternate is used on all OpenBSD, pending contribution
> of an appropriate preprocessor conditional. It also remains to
> determine versions and write a conditional for Solaris.

I've added this patch with the OpenBSD version guard here locally -- and
did you intend to add a Signed-off-by?

[Greg Troxel]

Rob Browning <r...@defaultvalue.org> writes:

> Greg Troxel <g...@lexort.com> writes:
>
>> realpath(3) originally required a non-NULL 2nd argument. POSIX
>> extended it to allow NULL, but some old BSD versions still have the
>> as-first-introduced-in-4.4BSD implementation that does not accept the
>> 2nd argument being NULL.
>>
>> Define bup_realpath, which collapses to just system realpath for most
>> systems, and on systems known to have historic realpath, use a buffer,
>> and strdup the results, to match the POSIX-with-NULL semantics.
>>
>> Currently the alternate is used on all OpenBSD, pending contribution
>> of an appropriate preprocessor conditional. It also remains to
>> determine versions and write a conditional for Solaris.
>
> I've added this patch with the OpenBSD version guard here locally -- and
> did you intend to add a Signed-off-by?

Yes, sorry, I definitely meant Signed-off-by and keep forgetting.

The OpenBSD version guard seems fine. Certainly if anybody on OpenBSD
figures out that it should be different, that's easy to change.

[Rob Browning]

Greg Troxel <g...@lexort.com> writes:

> Yes, sorry, I definitely meant Signed-off-by and keep forgetting.
>
> The OpenBSD version guard seems fine. Certainly if anybody on OpenBSD
> figures out that it should be different, that's easy to change.

Right, and thanks. I'll include this soon.

[Rob Browning]

From: Greg Troxel <g...@lexort.com>

realpath(3) originally required a non-NULL 2nd argument. POSIX
extended it to allow NULL, but some old BSD versions still have the
as-first-introduced-in-4.4BSD implementation that does not accept the
2nd argument being NULL.

Define bup_realpath, which collapses to just system realpath for most
systems, and on systems known to have historic realpath, use a buffer,
and strdup the results, to match the POSIX-with-NULL semantics.

This should fix NetBSD and OpenBSD, and realpath isn't used on
FreeBSD. This does not attempt to address Solaris.

Signed-off-by: Greg Troxel <g...@lexort.com>
Reviewed-by: Rob Browning <r...@defaultvalue.org>
[r...@defaultvalue.org: adjust commit message]
[r...@defaultvalue.org: change #define to BUP_HAVE_POSIX_REALPATH]
[r...@defaultvalue.org: add OpenBSD version guard clause]
[r...@defaultvalue.org: nest NetBSD checks so Prereq doesn't crash elsewhere]
[r...@defaultvalue.org: reformat bup_realpath a bit]
Signed-off-by: Rob Browning <r...@defaultvalue.org>
Tested-by: Rob Browning <r...@defaultvalue.org>
---

Pushed.

lib/cmd/bup.c | 46 +++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 43 insertions(+), 3 deletions(-)

diff --git a/lib/cmd/bup.c b/lib/cmd/bup.c
index 9cd1f388..0d002a91 100644
--- a/lib/cmd/bup.c
+++ b/lib/cmd/bup.c
@@ -96,6 +96,46 @@ setup_bup_main_module(void) {

die(2, "unable to register bup_main module\n");
}

+/*

+ * Older realpath implementations (e.g. 4.4BSD) required the second
+ * argument to be non-NULL, and then POSIX added the option of NULL
+ * with the semantics of malloc'ing a big-enough buffer. Define a
+ * helper function with the NULL semantics to accomodate older
+ * platforms.

+ *
+ * gnulib has a list of systems that are known to reject NULL as the
+ * 2nd argument:
+ * https://www.gnu.org/software/gnulib/manual/html_node/realpath.html
+ */
+

+#define BUP_HAVE_POSIX_REALPATH
+
+// FreeBSD < 7: bup's FreeBSD code does not use realpath(3)
+#if defined(__NetBSD__)
+# if !__NetBSD_Prereq__(7,0,0)
+# undef BUP_HAVE_POSIX_REALPATH
+# endif
+// OpenBSD: https://cvsweb.openbsd.org/cgi-bin/cvsweb/src/sys/sys/param.h.diff?r1=1.91&r2=1.92&f=h
+#elif defined(__OpenBSD__) && __OpenBSD__ < 201111
+# undef BUP_HAVE_POSIX_REALPATH
+#endif

+
+char *
+bup_realpath(const char *pathname)
+{

+#ifdef BUP_HAVE_POSIX_REALPATH

+ return realpath(pathname, NULL);
+#else

+ char resolvedname[PATH_MAX];
+ char *ret = realpath(pathname, resolvedname);

+ if (ret != NULL) {

+ assert(ret == resolvedname);
+ ret = strdup(ret);
+ }
+ return ret;
+#endif
+}
+
#if defined(__APPLE__) && defined(__MACH__)

static char *exe_parent_dir(const char * const argv_0) {

@@ -110,7 +150,7 @@ static char *exe_parent_dir(const char * const argv_0) {

}
if(rc != 0) die(2, "unable to find executable path\n");
char *path = mpath ? mpath : spath;
- char *abs_exe = realpath(path, NULL);
+ char *abs_exe = bup_realpath(path);
if (!abs_exe)
die(2, "cannot resolve path (%s): %s\n", strerror(errno), path);
char * const abs_parent = strdup(dirname(abs_exe));

@@ -215,7 +255,7 @@ static char *find_exe_parent(const char * const argv_0)

argv_0);
char *path_exe = find_in_path(argv_0, env_path);
if (path_exe) {
- char * abs_exe = realpath(path_exe, NULL);
+ char * abs_exe = bup_realpath(path_exe);
if (!abs_exe)
die(2, "cannot resolve path (%s): %s\n",
strerror(errno), path_exe);

@@ -226,7 +266,7 @@ static char *find_exe_parent(const char * const argv_0)

if (!candidate)
return NULL;

- char * const abs_exe = realpath(candidate, NULL);
+ char * const abs_exe = bup_realpath(candidate);
if (!abs_exe)
die(2, "cannot resolve path (%s): %s\n", strerror(errno), candidate);
free(candidate);
--

2.30.2