On Mon, 07 Nov 2005 19:48:47 +0000, Gordon Burditt wrote:
>> [quoted text muted]
>
> There is no O_DIRECT or fcntl() in Standard C.
>
> fcntl() operates on an open file descriptor, and the file descriptor
> for stdin is 0. Two calls to fcntl(), one with F_GETFL and one
> with F_SETFL, would do what you want.
>
> I'm not sure why you want to do that, though. It's not going to
> get you character-at-a-time I/O, if that's what you want.
>
> Gordon L. Burditt
I want to be able to read a HUGE file without having such a negative
impact on the system's buffer cache.
I'm trying:
if hasattr(os, 'O_DIRECT'):
try:
flags = fcntl.fcntl(sys.stdin.fileno(), fcntl.F_GETFL)
flags |= os.O_DIRECT
fcntl.fcntl(sys.stdin.fileno(), fcntl.F_SETFL, flags)
except:
sys.stderr.write('Setting O_DIRECT on stdin attempted
but failed\n')
else:
sys.stderr.write('Setting O_DIRECT on stdin succeeded
:)\n')
...but while this code doesn't error out, I get:
seki-root> reblock -e $[1024*1024*80] $[1024*1024] 300 < /dev/sda1 > /dev/null
stdin seems seekable, but file length is 0 - no exact percentages
Estimated filetransfer size is 85899345920 bytes
Estimated percentages will only be as accurate as your size estimate
Setting O_DIRECT on stdin succeeded :)
Traceback (most recent call last):
File "/Dcs/seki/strombrg/bin/reblock", line 276, in ?
main()
File "/Dcs/seki/strombrg/bin/reblock", line 222, in main
block = os.read(0,blocksize)
OSError: [Errno 22] Invalid argument
Mon Nov 07 12:25:53
...but if I comment out the fcntl/O_DIRECT code, then the same thing works
well.
Any other ideas folks?
Thanks!
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