[xen staging] tools/xenpmd: Fix gcc10 snprintf warning

[patchbot@xxxxxxx]

commit 0dfddb2116e3757f77a691a3fe335173088d69dc
Author:     Bertrand Marquis <bertrand.marquis@xxxxxxx>
AuthorDate: Thu Oct 15 10:16:09 2020 +0100
Commit:     Wei Liu <wl@xxxxxxx>
CommitDate: Fri Oct 16 13:28:55 2020 +0000

    tools/xenpmd: Fix gcc10 snprintf warning
    
    Add a check for snprintf return code and ignore the entry if we get an
    error. This should in fact never happen and is more a trick to make gcc
    happy and prevent compilation errors.
    
    This is solving the following gcc warning when compiling for arm32 host
    platforms with optimization activated:
    xenpmd.c:92:37: error: '%s' directive output may be truncated writing
    between 4 and 2147483645 bytes into a region of size 271
    [-Werror=format-truncation=]
    
    This is also solving the following Debian bug:
    https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=970802
    
    Signed-off-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
    Acked-by: Wei Liu <wl@xxxxxxx>
---
 tools/xenpmd/xenpmd.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/tools/xenpmd/xenpmd.c b/tools/xenpmd/xenpmd.c
index 35fd1c931a..12b82cf43e 100644
--- a/tools/xenpmd/xenpmd.c
+++ b/tools/xenpmd/xenpmd.c
@@ -102,6 +102,7 @@ FILE *get_next_battery_file(DIR *battery_dir,
     FILE *file = 0;
     struct dirent *dir_entries;
     char file_name[284];
+    int ret;
     
     do 
     {
@@ -111,11 +112,15 @@ FILE *get_next_battery_file(DIR *battery_dir,
         if ( strlen(dir_entries->d_name) < 4 )
             continue;
         if ( battery_info_type == BIF ) 
-            snprintf(file_name, sizeof(file_name), BATTERY_INFO_FILE_PATH,
+            ret = snprintf(file_name, sizeof(file_name), 
BATTERY_INFO_FILE_PATH,
                      dir_entries->d_name);
         else 
-            snprintf(file_name, sizeof(file_name), BATTERY_STATE_FILE_PATH,
+            ret = snprintf(file_name, sizeof(file_name), 
BATTERY_STATE_FILE_PATH,
                      dir_entries->d_name);
+        /* This should not happen but is needed to pass gcc checks */
+        if (ret < 0)
+            continue;
+        file_name[sizeof(file_name) - 1] = '\0';
         file = fopen(file_name, "r");
     } while ( !file );
 
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