Hello Michael,

the sentence in open(2) man page in notes for O_DIRECT flag:
"Under Linux 2.6, alignment to 512-byte boundaries suffices."

is not universally correct. The alignment is a property of the storage, 
for example, 4k-sector drives with no 512 byte sector emulation will be 
unable to perform 512-byte direct I/O.

The patch clarifies this sentence.

Thanks,

peter