Date: Tue, 1 Jun 2004 19:10:19 -0700 (PDT) From: "David G. Andersen" <dga@lcs.mit.edu> To: freebsd-bugs@FreeBSD.org Subject: Re: bin/67467: df -m and -g incorrect with negative avail Message-ID: <200406020210.i522AJVY034650@freefall.freebsd.org>
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The following reply was made to PR bin/67467; it has been noted by GNATS. From: "David G. Andersen" <dga@lcs.mit.edu> To: freebsd-gnats-submit@FreeBSD.org, dga@lcs.mit.edu Cc: Subject: Re: bin/67467: df -m and -g incorrect with negative avail Date: Tue, 1 Jun 2004 22:08:14 -0400 The problem is with the fsbtoblk macro on line 401 of /usr/src/bin/df.c #define fsbtoblk(num, fsbs, bs) \ (((fsbs) != 0 && (fsbs) < (bs)) ? \ (num) / ((bs) / (fsbs)) : (num) * ((fsbs) / (bs))) The problem only occurs when the user specifies a blocksize larger than the filesystem blocksize (probably 4k), invoking this part of the code: (num) / ((bs) / (fsbs)) Unfortunately, the result of this is of the type of fsbs (which is a u_int64_t), instead of being of the type of num (int64_t). The easiest solution is an explicit cast in the macro: (num) / (intmax_t)((bs) / (fsbs)) : (num) * ((fsbs) / (bs))) This could result in a premature cast out of unsignedness iff fsbs = 1 and bs > 2^63 and num is an unsigned quantity, but it's safe in other situations. If gcc extensions are kosher, then it would better be written as: (num) / (typeof(num))((bs) / (fsbs)) : (num) * ((fsbs) / (bs))) since typeof seems to be used elsewhere in the kernel, I assume this is acceptable.
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