[Xen-devel] [PATCH] check read/write return values

[Rik van Riel <riel@xxxxxxxxxx>]

The Fedora build system is in paranoid mode, and compiles everything
with -Werror.  Additionally, it checks that the return values of calls
like read and write are checked.

The build exits with errors like:

xen/lowlevel/xc/xc.c: In function `pyxc_vmx_build':
xen/lowlevel/xc/xc.c:464: warning: ignoring return value of `sscanf', declared 
with attribute warn_unused_result
xen/lowlevel/xc/xc.c:465: warning: ignoring return value of `sscanf', declared 
with attribute warn_unused_result
error: command 'gcc' failed with exit status 1

This (trivial) patch, against yesterday's unstable snapshot, adds
these checks for a number of functions.  The obvious exception is
the dumpit function, which isn't called by anybody anyway.

I have verified that Xen still boots and can create Linux domains
with these changes applied.  I tried to stick to the various coding
styles in the different files.

Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>

--- xen-unstable/tools/libxc/xc_plan9_build.c.warn      2005-02-19 
11:58:24.000000000 -0500
+++ xen-unstable/tools/libxc/xc_plan9_build.c   2005-02-19 12:02:41.000000000 
-0500
@@ -63,6 +63,7 @@
  * your image builder.
  * Xen guys, nuke this if you wish.
  */
+#if 0 /* NOT CALLED */
 void
 dumpit(int xc_handle, u32 dom,
        int start_page, int tot, unsigned long *page_array)
@@ -85,6 +86,7 @@
                munmap(vaddr, PAGE_SIZE);
        }
 }
+#endif
 int
 blah(char *b)
 {
--- xen-unstable/tools/libxc/xc_private.c.warn2 2005-02-19 12:12:44.000000000 
-0500
+++ xen-unstable/tools/libxc/xc_private.c       2005-02-19 12:14:44.000000000 
-0500
@@ -276,12 +276,14 @@
     unsigned long sz;

     lseek(fd, 0, SEEK_SET);
-    read(fd, &sig, sizeof(sig));
+    if ( read(fd, &sig, sizeof(sig)) != sizeof(sig) )
+       return 0;
     sz = lseek(fd, 0, SEEK_END);
     if ( sig == 0x8b1f ) /* GZIP signature? */
     {
         lseek(fd, -4, SEEK_END);
-        read(fd, &_sz, 4);
+        if ( read(fd, &_sz, 4) != 4 )
+               return 0;
         sz = _sz;
     }
     lseek(fd, 0, SEEK_SET);
@@ -304,6 +306,12 @@

     *size = xc_get_filesz(kernel_fd);

+    if ( *size == 0 )
+    {
+        PERROR("Could not read kernel image");
+        goto out;
+    }
+
     if ( (kernel_gfd = gzdopen(kernel_fd, "rb")) == NULL )
     {
         PERROR("Could not allocate decompression state for state file");
--- xen-unstable/tools/xentrace/xentrace.c.warn 2005-02-19 12:31:19.994379665 
-0500
+++ xen-unstable/tools/xentrace/xentrace.c      2005-02-19 12:37:11.425091593 
-0500
@@ -77,8 +77,14 @@ struct timespec millis_to_timespec(unsig
  */
 void write_rec(unsigned int cpu, struct t_rec *rec, FILE *out)
 {
-    fwrite(&cpu, sizeof(cpu), 1, out);
-    fwrite(rec, sizeof(*rec), 1, out);
+    size_t written = 0;
+    written += fwrite(&cpu, sizeof(cpu), 1, out);
+    written += fwrite(rec, sizeof(*rec), 1, out);
+    if ( written != 2 )
+    {
+        PERROR("Failure to write trace record");
+        exit(EXIT_FAILURE);
+    }
 }

 /**
--- xen-unstable/tools/python/xen/lowlevel/xc/xc.c.warn 2005-02-19 
13:10:45.558410335 -0500
+++ xen-unstable/tools/python/xen/lowlevel/xc/xc.c      2005-02-19 
14:21:19.323167162 -0500
@@ -461,8 +461,10 @@ static PyObject *pyxc_vmx_build(PyObject
            sf2 = PyString_AsString(f2);
            lf3 = PyLong_AsLong(f3);
            lf4 = PyLong_AsLong(f4);
-           sscanf(sf1, "%lx", &lf1);
-           sscanf(sf2, "%lx", &lf2);
+           if (sscanf(sf1, "%lx", &lf1) != 1)
+               return NULL;
+           if (sscanf(sf2, "%lx", &lf2) != 1)
+               return NULL;

             mem_map.map[i-1].addr = lf1;
             mem_map.map[i-1].size = lf2 - lf1;


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