> Date: Wed, 21 Feb 2024 10:52:55 +0000 > From: Sad Clouds <cryintotheblue...@gmail.com> > > Hello, for most operating systems determining the size of a block > device can be done with: > > lseek(fd, 0, SEEK_END); > > However, on NetBSD this does not seem to work.
Internally, this is happens for more or less the same reason that stat(2) doesn't return the size of a block device in st_size. Each file system on which device nodes can reside implements its own VOP_GETATTR (used by both lseek(2) and stat(2)), and most of them use the _inode_ size (more or less) rather than querying the block device that the device node represents for its physical size. I think this is a bug, and it would be great if stat(2) just returned the physical medium's size in st_size -- currently doing this reliably takes at least three different ioctls to handle all storage media, if I counted correctly in sbin/fsck/partutil.c's getdiskinfo. But it's a little annoying to make that happen because it requires going through all the file systems that have device nodes and convincing their VOP_GETATTR implementations to do something different for block devices (and ideally also character devices, if they represent fixed-size media too).
