FAT32 statfs(2) inode usage

Hi Everyone,

I'm using Netdata to monitor my FreeBSD systems, and it is reporting critical alerts that my UEFI system partition has run out of available inodes. Investigating a bit further, I realised that the FreeBSD df(1) utility is reporting the same, meaning this is a FreeBSD bug rather than a Netdata bug.

$ df -i /boot/efi
Filesystem  512-blocks Used  Avail Capacity iused ifree %iused  Mounted on
/dev/nvd0p1     532352 3680 528672     1%     512     0  100%   /boot/efi

It looks like this stems from the following section of the msdosfs(5) driver code sys/fs/msdosfs/msdosfs_vfsops.c:
----------------------------
static int
msdosfs_statfs(struct mount *mp, struct statfs *sbp)
{
	struct msdosfsmount *pmp;

	pmp = VFSTOMSDOSFS(mp);
	sbp->f_bsize = pmp->pm_bpcluster;
	sbp->f_iosize = pmp->pm_bpcluster;
	sbp->f_blocks = pmp->pm_maxcluster + 1;
	sbp->f_bfree = pmp->pm_freeclustercount;
	sbp->f_bavail = pmp->pm_freeclustercount;
	sbp->f_files = pmp->pm_RootDirEnts;	/* XXX */
	sbp->f_ffree = 0;	/* what to put in here? */
	return (0);
}
----------------------------

I think it might be more correct for msdosfs_vfsops.c to set the f_files variable to 0. Thoughts on this change?

This would then cause the following df(1) code to report iused% as "-" rather than "100%":
----------------------------
inodes = sfsp->f_files;
used = inodes - sfsp->f_ffree;
...
if (inodes == 0)
	xo_emit(" {:inodes-used-percent/    -}{U:} ");
else {
	xo_emit(" {:inodes-used-percent/%4.0f}{U:%%} ",
		(double)used / (double)inodes * 100.0);
}
----------------------------

This would then give an df(1) output which is consistent with GNU/Linux - see below test results from Debian 11:
# df -i /mnt/fat32
Filesystem     Inodes IUsed IFree IUse% Mounted on
/dev/vdb1           0     0     0     - /mnt/fat32

Regards,
Ben

--
From: Ben Woods
woodsb02@freebsd.org