O_DIRECT alignment requirements ?

[Rob van Nieuwkerk]

Hi all,

I plan to use O_DIRECT in my application (on a partition, no fs).
It is hard to find info on the exact requirements on the mandatory
alignments of buffer, offset, transfer size: it's easy to find many
contradicting documents.  And checking the kernel source itself isn't
trivial.

lseek(int fildes, off_t offset, int whence);
read(int fd, void *buf, size_t count);

My current assumption is this:

	- offset must be block_aligned (multiple of 512)
	- buf must be page_aligned (4096 on IA32)
	- count must be "block_aligned" (multiple of 512)

Is this correct ?

	r.

sysinfo:
--------
- Linux 2.4 (recent versions)
- using raw partion, no files, no fs
- IA32