cdrom driver dependency problem (and a workaround patch)

From: Dan Aloni (karrde@callisto.yi.org)
Date: Fri Apr 20 2001 - 18:17:18 EST

Between 2.4.3-ac9 and 2.4.3-ac10 the CDROM Uniform Driver was modified.
The modification added a dependency of the *register_cdrom() functions
on the cdrom_init() function. Theoretically, cdrom_init() should have
been called before any call to register_cdrom(). But practically, when
the CDROM driver is compiled into the kernel and not as a module, it
doesn't happen, and in 2.4.3-ac10 you get an Oops in cdrom_get_entry(),
where the NULL cdrom_numbers gets dereferenced.

One reason for this misdependency is that the IDE is initialized before
the cdrom driver, register_cdrom() gets called from inside the IDE
initialization functions. (ide_init() -> ide_init_builtin_drivers() ->
ide_cdrom_init() -> ide_cdrom_setup() -> ide_cdrom_register() ->
register_cdrom())

In order to get my kernel to boot, I've made the following temporary
workaround patch. I'd be glad to hear about other ways of solving this.

--- linux-2.4.3-ac10/drivers/cdrom/cdrom.c Fri Apr 20 23:38:37 2001
+++ linux-2.4.3-ac10/drivers/cdrom/cdrom.c Sat Apr 21 01:59:35 2001
@@ -277,6 +277,7 @@
 static int autoclose=1;
 static int autoeject;
 static int lockdoor = 1;
+static int initialized;
 /* will we ever get to use this... sigh. */
 static int check_media_type;
 static unsigned long *cdrom_numbers;
@@ -332,6 +333,9 @@
 #ifdef CONFIG_SYSCTL
 static void cdrom_sysctl_register(void);
 #endif /* CONFIG_SYSCTL */
+
+static int check_cdrom_init(void);
+
 static struct cdrom_device_info *topCdromPtr;
 static devfs_handle_t devfs_handle;

@@ -350,6 +354,8 @@
 {
         int i, nr, foo;

+ printk("Holly damn. cdrom_numbers=0x%p\n",cdrom_numbers);
+
         nr = 0;
         foo = -1;
         for (i = 0; i < CDROM_MAX_CDROMS / (sizeof(unsigned long) * 8); i++) {
@@ -368,7 +374,7 @@

 static void cdrom_clear_entry(struct cdrom_device_info *cdi)
 {
- int bit_nr = cdi->nr & ~(sizeof(unsigned long) * 8);
+ int bit_nr = cdi->nr % (sizeof(unsigned long) * 8);
         int cd_index = cdi->nr / (sizeof(unsigned long) * 8);

         clear_bit(bit_nr, &cdrom_numbers[cd_index]);
@@ -388,10 +394,14 @@
         int major = MAJOR(cdi->dev);
         struct cdrom_device_ops *cdo = cdi->ops;
         int *change_capability = (int *)&cdo->capability; /* hack */
+ int rc;
         char vname[16];

         cdinfo(CD_OPEN, "entering register_cdrom\n");

+ if ((rc = check_cdrom_init()) != 0)
+ return rc;
+
         if (major < 0 || major >= MAX_BLKDEV)
                 return -1;
         if (cdo->open == NULL || cdo->release == NULL)
@@ -2706,11 +2716,29 @@

 #endif /* CONFIG_SYSCTL */

-static int __init cdrom_init(void)
+static int check_cdrom_init(void)
 {
- int n_entries = CDROM_MAX_CDROMS / (sizeof(unsigned long) * 8);
+ if (!initialized)
+ {
+ int n_entries;
+
+ initialized = 1;
+ n_entries = CDROM_MAX_CDROMS / (sizeof(unsigned long) * 8);

- cdrom_numbers = kmalloc(n_entries * sizeof(unsigned long), GFP_KERNEL);
+ cdrom_numbers = kmalloc(n_entries * sizeof(unsigned long), GFP_KERNEL);
+
+ if (cdrom_numbers == NULL)
+ return -ENOMEM;
+ }
+ return 0;
+}
+
+static int __init cdrom_init(void)
+{
+ int rc;
+
+ if ((rc = check_cdrom_init()) != 0)
+ return rc;

 #ifdef CONFIG_SYSCTL
         cdrom_sysctl_register(); 

--
Dan Aloni
dax@karrde.org

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This archive was generated by hypermail 2b29 : Mon Apr 23 2001 - 21:00:38 EST