Samba reports incorrect used disk space on Windows XP.

Zack Kirsch zkirsch at
Sat Feb 5 01:16:06 GMT 2005

Repro: From Windows XP, connect to a Samba 3.x server exporting a nearly
empty filesystem.  Query the used space of the share's filesystem via
<right click->Properties.  Observe that the used space is zero.  

tcpdump confirms that the issue lies with the Trans2 -> QUERY_FS_INFO
response and not with the client.

It appears that Samba rounds down used space under certain
circumstances.  On large filesystems (billions of blocks) used space
rounded down quite substantially: 32MB in our case.  Smaller filesystems
will exhibit smaller rounding error and some will not exhibit rounding
issues at all.

I believe the problem lies with dfree.c:disk_norm(), called via
vfswrap_disk_free()->sys_disk_free()->disk_free().  Specifically, this
function scales dfree (disk free), dsize (total filesystem size) and
bsize (block size) such that they can be represented using sixteen bits
or less.  This results in a loss of precision for large values.  Such
behavior is particularly odd given that a QUERY_FS_INFO response will
renormalize these numbers again as needed to support lp_block_size(),
and that the on-the-wire representations are 32 bit and 64 bit

disk_norm() appears to be obsolete logic, or at least not appropriate
for Windows, as the function's stated purpose is to "normalise for DOS

It seems like the disk_norm() function is obsolete or used too broadly.
Can it safely be removed from the Trans2 QUERY_FS_INFO path?

Heres the bug that I filed on it:

Zack Kirsch

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