On Thu, 22 Mar 2007, Mike Frysinger wrote: > On 3/22/07, Robert P. J. Day <rpjday@xxxxxxxxxxxxxx> wrote: > > given that the current definition of a major device number is a > > 12-bit value (include/linux/kdev_t.h), is there any reason that > > dynamic allocation of major numbers via alloc_chrdev_region() limits > > itself based on the value of > > > > include/linux/fs.h:#define CHRDEV_MAJOR_HASH_SIZE 255 > > > > sure, i realize there's no real danger of running out of major > > numbers, but i'm just curious. i'm wondering what other places in the > > source tree might have a hard-coded value of 255 for that. > > probably historical ? dev_t wasnt always as large as it is now ... > -mike oh, i realize *that*. i was just wondering why the definition of CHRDEV_MAJOR_HASH_SIZE wasn't keeping up with the definition of kdev_t. actually, more curiously, i'm wondering if i should be nervous about the inconsistent definitions of the macros in kdev_t.h: ... #ifdef __KERNEL__ #define MINORBITS 20 #define MINORMASK ((1U << MINORBITS) - 1) #define MAJOR(dev) ((unsigned int) ((dev) >> MINORBITS)) #define MINOR(dev) ((unsigned int) ((dev) & MINORMASK)) #define MKDEV(ma,mi) (((ma) << MINORBITS) | (mi)) ... #else /* __KERNEL__ */ /* Some programs want their definitions of MAJOR and MINOR and MKDEV from the kernel sources. These must be the externally visible ones. */ #define MAJOR(dev) ((dev)>>8) #define MINOR(dev) ((dev) & 0xff) #define MKDEV(ma,mi) ((ma)<<8 | (mi)) #endif /* __KERNEL__ */ ... so the definition of MAJOR() and MINOR() in kernel space is based on a 12/20 split of major/minor device number, while the *user* space definitions are still based on the historical 8/8 split. does anyone else find this a bit odd? rday -- ======================================================================== Robert P. J. Day Linux Consulting, Training and Annoying Kernel Pedantry Waterloo, Ontario, CANADA http://fsdev.net/wiki/index.php?title=Main_Page ======================================================================== -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
