[PATCH] kexec/fs2dt.c: wrong dt node fix

[Dave Young]

There is a report for ppc64le kexec fail in below Fedora 23 bug:
https://bugzilla.redhat.com/show_bug.cgi?id=1310495

2nd kernel hangs early because of a regression caused by below commit:
commit 68262155d8c661586b809bc5301a7dff1c378137
Author: Andrew Jones <drjones at redhat.com>
Date:   Fri Nov 20 12:31:53 2015 -0500

    kexec/fs2dt: cleanup pathname
    
    putnode() will add the trailing '/', avoid having two. Also
    pathstart is unused, get rid of it.
    
    Signed-off-by: Andrew Jones <drjones at redhat.com>
    Signed-off-by: Simon Horman <horms at verge.net.au>

The actual purpose of the commit is to avoid double slash in pathname.
But unfortunately in function putnode() we have below magics to get the node
name:
	basename = strrchr(pathname,'/') + 1;
	...
	strcpy((void *)dt, *basename ? basename : "");
	...
	strcat(pathname, "/");

We treat none zero basename as a node name, then concat a slash to open the
directory for later property handling.
pathname originally was "/proc/device-tree/" so for the first run of putnode
it will cause double slashes. With the commit above mentioned there are no
double slashes but we will copy "device-tree" to dt. Thus kexec kernel is not
happy..

Instead let's fix it by only concating slash when the basenanme is not empty
and restore the initial value of pathname as "/proc/device-tree/"

Signed-off-by: Dave Young <dyoung at redhat.com>
---
 kexec/fs2dt.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- kexec-tools.orig/kexec/fs2dt.c
+++ kexec-tools/kexec/fs2dt.c
@@ -577,7 +577,8 @@ static void putnode(void)
 	strcpy((void *)dt, *basename ? basename : "");
 	dt += ((plen + 4)/4);
 
-	strcat(pathname, "/");
+	if (*basename)
+		strcat(pathname, "/");
 	dn = pathname + strlen(pathname);
 
 	putprops(dn, namelist, numlist);
@@ -804,7 +805,7 @@ static void add_boot_block(char **bufp,
 
 void create_flatten_tree(char **bufp, off_t *sizep, const char *cmdline)
 {
-	strcpy(pathname, "/proc/device-tree");
+	strcpy(pathname, "/proc/device-tree/");
 
 	dt_cur_size = INIT_TREE_WORDS;
 	dt_base = malloc(dt_cur_size*4);