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Illegal seek error with seek() and os.lseek() in python

0 votes
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I am trying to use os.open() and os.lseek() methods to operate on a device file in Linux. My code goes something like this -

# first, open the file as a plain binary
try:
self.file = open(/dev/relpcfpga, "r+b", buffering=0)

except IOError:
raise IOError ('Failed to open.')

# Figure out file size
self.file.seek(0, 2)
self.file_size = self.file.tell()

The method seek() complains "OSError: [Errno 29] Illegal seek"
The device relpcfpga is a char device.

The same code works with a normal text file.
I have tried to use os.open() and os.lseek() methods, but see the same error.
Is there a different method to operate on device files?

posted May 14, 2013 by anonymous

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1 Answer

0 votes

Some file streams are not seekable. Specifically, some (all?) char
devices aren't seekable (because e.g. they can't be rewound or they have
no end). You'd get the same error in C (well it would return -1).

See also: http://www.linuxintro.org/wiki/Device

answer May 14, 2013 by anonymous
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