Date: Fri, 12 Apr 2019 09:10:58 -0600 From: Alan Somers <asomers@freebsd.org> To: FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: When can a struct buf's b_lblkno field by < 0 ? Message-ID: <CAOtMX2iUqx3T-VNrj=KkpvWn0AFti-ZoGTL87EewiwNKWi7byw@mail.gmail.com>
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In struct buf, b_lblkno is documented as "Logical block number". I
would expect that to always be nonnegative. However, vtruncbuf loops
through a list of buffers, skipping those where "bp->b_lblkno > 0".
Maybe that's just an awkward way of writing "do something for the
buffer where b_lblkno == 0", but SVN archaeology suggests otherwise.
Before r112182, the code looked like this, implying that the b_lblkno
could actually be negative:
if ((bp->b_flags & B_DELWRI) && (bp->b_lblkno < 0)) {
Does anybody know under what circumstances that field might be
negative? Also, was r112182 a correct change? It appears to have
negated "<" and gotten ">", neglecting the "==" case.
https://svnweb.freebsd.org/base/head/sys/kern/vfs_subr.c?r1=112182&r2=112181&pathrev=112182
-Alan
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