nshlib: added cmp command to nsh

this is useful for startup scripts testing for auto-upgrade of add-on 
board firmware

apps/nshlib/Kconfig

@@ -55,6 +55,10 @@ config NSH_DISABLE_CP
 	bool "Disable cp"
 	default n
 
+config NSH_DISABLE_CMP
+	bool "Disable cmp"
+	default n
+
 config NSH_DISABLE_DD
 	bool "Disable dd"
 	default n

apps/nshlib/nsh.h

@@ -603,6 +603,9 @@ void nsh_usbtrace(void);
 #  ifndef CONFIG_NSH_DISABLE_CP
       int cmd_cp(FAR struct nsh_vtbl_s *vtbl, int argc, char **argv);
 #  endif
+#  ifndef CONFIG_NSH_DISABLE_CMP
+      int cmd_cmp(FAR struct nsh_vtbl_s *vtbl, int argc, char **argv);
+#  endif
 #  ifndef CONFIG_NSH_DISABLE_DD
       int cmd_dd(FAR struct nsh_vtbl_s *vtbl, int argc, char **argv);
 #  endif

apps/nshlib/nsh_fscmds.c

@@ -1232,3 +1232,84 @@ int cmd_sh(FAR struct nsh_vtbl_s *vtbl, int argc, char **argv)
 }
 #endif
 #endif
+
+
+#if CONFIG_NFILE_DESCRIPTORS > 0
+#ifndef CONFIG_NSH_DISABLE_CMP
+int cmd_cmp(FAR struct nsh_vtbl_s *vtbl, int argc, char **argv)
+{
+  char *path1 = NULL;
+  char *path2 = NULL;
+  int fd1 = -1, fd2 = -1;
+  int ret = ERROR;
+  unsigned total_read = 0;
+
+  /* Get the full path to the two files */
+
+  path1 = nsh_getfullpath(vtbl, argv[1]);
+  if (!path1)
+    {
+      goto errout;
+    }
+
+  path2 = nsh_getfullpath(vtbl, argv[2]);
+  if (!path2)
+    {
+      goto errout;
+    }
+
+  /* Open the files for reading */
+  fd1 = open(path1, O_RDONLY);
+  if (fd1 < 0)
+    {
+      nsh_output(vtbl, g_fmtcmdfailed, argv[0], "open", NSH_ERRNO);
+      goto errout;
+    }
+
+  fd2 = open(path2, O_RDONLY);
+  if (fd2 < 0)
+    {
+      nsh_output(vtbl, g_fmtcmdfailed, argv[0], "open", NSH_ERRNO);
+      goto errout;
+    }
+
+  for (;;)
+    {
+      char buf1[128];
+      char buf2[128];
+
+      int nbytesread1 = read(fd1, buf1, sizeof(buf1));
+      int nbytesread2 = read(fd2, buf2, sizeof(buf2));
+
+      if (nbytesread1 < 0)
+          {
+	      nsh_output(vtbl, g_fmtcmdfailed, argv[0], "read", NSH_ERRNO);
+	      goto errout;
+	  }
+
+      if (nbytesread2 < 0)
+          {
+	      nsh_output(vtbl, g_fmtcmdfailed, argv[0], "read", NSH_ERRNO);
+	      goto errout;
+	  }
+
+      total_read += nbytesread1>nbytesread2?nbytesread2:nbytesread1;
+
+      if (nbytesread1 != nbytesread2 || memcmp(buf1, buf2, nbytesread1) != 0)
+          {
+	      nsh_output(vtbl, "files differ: byte %u\n", total_read);
+              goto errout;
+          }
+
+      if (nbytesread1 < sizeof(buf1)) break;
+    }
+
+  ret = OK;
+
+errout:
+  if (fd1 != -1) close(fd1);
+  if (fd2 != -1) close(fd2);
+  return ret;
+}
+#endif
+#endif

apps/nshlib/nsh_parse.c

@@ -175,6 +175,9 @@ static const struct cmdmap_s g_cmdmap[] =
 # ifndef CONFIG_NSH_DISABLE_CP
   { "cp",       cmd_cp,       3, 3, "<source-path> <dest-path>" },
 # endif
+# ifndef CONFIG_NSH_DISABLE_CMP
+  { "cmp",      cmd_cmp,      3, 3, "<path1> <path2>" },
+# endif
 #endif
 
 #if defined (CONFIG_RTC) && !defined(CONFIG_DISABLE_CLOCK) && !defined(CONFIG_NSH_DISABLE_DATE)