Messages in this thread | | | From | Andreas Dilger <> | Date | Fri, 14 Jun 2002 21:37:24 -0600 | Subject | Re: 2.4.18 kernel lseek() bug |
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On Jun 14, 2002 15:07 +0200, Tomaz Susnik wrote: > [1] Problem description > ---------------------------------- > > a call to lseek() fails with EINVAL under the following conditions: > - it is called on a disk device file > - required offset is larger than the target disk device size
Is this behaviour mandated in a standard, or is it just different from previous behaviour? I'm not saying it _isn't_ a bug, but I don't see how seeking past the end of a block device is very useful.
> Attempting to seek through file /dev/hda3 > > lseek(6 Gb ): errno = 0 ret = 6442450944 > lseek(7 Gb ): errno = 0 ret = 7516192768 > lseek(8 Gb ): errno = 0 ret = 8589934592 > lseek(9 Gb ): errno = 0 ret = 9663676416 > > > Sample output on the same machine, but booted with kernel 2.4.18: > > Attempting to seek through file /dev/hda3 > > lseek(6 Gb ): errno = 0 ret = 6442450944 > lseek(7 Gb ): errno = 0 ret = 7516192768 > lseek(8 Gb ): errno = 22 ret = -1 > lseek(9 Gb ): errno = 22 ret = -1 > > [6] Reason for reporting this problem > --------------------------------------------------- > Our multi-platform backup product relies on proper behaviour of the > lseek() command to calculate a rawdisk size.
Well, e2fsprogs has a similar test that it uses if the BLKGETSZ ioctl fails, but I don't see how this new behaviour is a real problem. All you have to do is check if _either_ lseek(offset) fails or read() from that offset fails to know you are past the end of the block device. It hardly changes the algorithm at all.
Cheers, Andreas -- Andreas Dilger http://www-mddsp.enel.ucalgary.ca/People/adilger/ http://sourceforge.net/projects/ext2resize/
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