Rough? You mean "approximate"? I was working from my vague mamory of
what I read in the code on the train this morning.
> > It looks like the 2.5 kernel has this pathway, but what about the 2.4
> > kernel? Nothing.
> The manpage claims:
> This flag is supported on a number of Unix-like systems;
> support was added under Linux in kernel version 2.4.10.
My manpage for open(2) claims no such thing. It doesn't mention
O_DIRECT. Maybe your libc6 is newer.
In any case, it doesn't make it clear to me if I have to set the flag
in the driver. Well, anyway, I'll set it.
> A semantically similar interface for block devices is
> described in raw(8).
That's nothing like, since it's a character device that they were
describing. But yes, reading drivers/char/raw.c led me to see the
pathway via direct_IO() in 2.5.31, but in the 2.4.19 kernel the path is
obscure. In 2.5.31 it's clear that mm/filemap.c does pay attention to the
flag, and YES, you are right, in 2.4.19, generic_file_read() does
look at the flag. However, I have not much idea where that filp
comes from or what it represents. Oh, well, thanks.I suppose
you won't give me a recipe saying "do this and your device won't be
cached", but I'll follow the lead.
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