Thursday, May 13, 2010

LDD3 notes: Data types

My notes while reading Linux Device Drivers 3rd edition.

size_t vs ssize_t for negative values as error codes

C99 [u]intptr_t, integer which would fit a pointer. Not used in Linux. Similar to eCos cyg_addrword.

fixed size integers

  • u8..s32 within kernel
  • ioctl structures shared with userspace use prefix __u8

_t Typedefs

  • for portability only
  • out of fashion
  • inconvenient printk use

Important constants: HZ. PAGE_SIZE/SHIFT


  • cpu_to_le32() .. be64_to_cpu()


  • force struct to match hardware expectations, without padding for performance: __attribute__ ((packed))

Error codes in pointers

  • ERR_PTR() -> IS_ERR() -> PTR_ERR()


  • list_del_init() - re-init for future re-insertion
  • list_for_each_entry() - foreach and list_entry combined

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