Linux Device Drivers 3 examples

1 files changed, 58 insertions, 0 deletions

diff --git a/misc-progs/dataalign.c b/misc-progs/dataalign.c
new file mode 100644
index 0000000..1042ab7
--- /dev/null
+++ b/misc-progs/dataalign.c
@@ -0,0 +1,58 @@
+/*
+ * dataalign.c -- show alignment needs
+ *
+ * Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet
+ * Copyright (C) 2001 O'Reilly & Associates
+ *
+ * The source code in this file can be freely used, adapted,
+ * and redistributed in source or binary form, so long as an
+ * acknowledgment appears in derived source files.  The citation
+ * should list that the code comes from the book "Linux Device
+ * Drivers" by Alessandro Rubini and Jonathan Corbet, published
+ * by O'Reilly & Associates.   No warranty is attached;
+ * we cannot take responsibility for errors or fitness for use.
+ *
+ * This runs with any Linux kernel (not any Unix, because of <linux/types.h>)
+ */
+#include <stdio.h>
+#include <sys/utsname.h>
+#include <linux/types.h>
+
+/*
+ * Define several data structures, all of them start with a lone char
+ * in order to present an unaligned offset for the next field
+ */
+struct c   {char c;  char      t;} c;
+struct s   {char c;  short     t;} s;
+struct i   {char c;  int       t;} i;
+struct l   {char c;  long      t;} l;
+struct ll  {char c;  long long t;} ll;
+struct p   {char c;  void *    t;} p;
+struct u1b {char c;  __u8      t;} u1b;
+struct u2b {char c;  __u16     t;} u2b;
+struct u4b {char c;  __u32     t;} u4b;
+struct u8b {char c;  __u64     t;} u8b;
+
+int main(int argc, char **argv)
+{
+    struct utsname name;
+
+    uname(&name); /* never fails :) */
+    printf("arch  Align:  char  short  int  long   ptr long-long "
+	   " u8 u16 u32 u64\n");
+    printf(       "%-12s  %3i   %3i   %3i   %3i   %3i   %3i      "
+	   "%3i %3i %3i %3i\n",
+	   name.machine,
+	   /* note that gcc can subtract void * values, but it's not ansi */
+	   (int)((void *)(&c.t)   - (void *)&c),
+	   (int)((void *)(&s.t)   - (void *)&s),
+	   (int)((void *)(&i.t)   - (void *)&i),
+	   (int)((void *)(&l.t)   - (void *)&l),
+	   (int)((void *)(&p.t)   - (void *)&p),
+	   (int)((void *)(&ll.t)  - (void *)&ll),
+	   (int)((void *)(&u1b.t) - (void *)&u1b),
+	   (int)((void *)(&u2b.t) - (void *)&u2b),
+	   (int)((void *)(&u4b.t) - (void *)&u4b),
+	   (int)((void *)(&u8b.t) - (void *)&u8b));
+    return 0;
+}