Date: Tue, 29 Mar 2005 15:41:15 -0800 (PST) From: Richard Sharpe <rsharpe@richardsharpe.com> To: freebsd-hackers@freebsd.org Subject: Possible problems with mmap/munmap on FreeBSD ... Message-ID: <Pine.LNX.4.58.0503291533320.2471@durable>
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Hi,
I am having some problems with the tdb package on FreeBSD 4.6.2 and 4.10.
One of the things the above package does is:
mmap the tdb file to a region of memory
store stuff in the region (memmov etc).
when it needs to extend the size of the region {
munmap the region
write data at the end of the file
mmap the region again with a larger size
}
What I am seeing is that after the munmap the data written to the region
is gone.
However, if I insert an msync before the munmap, everything is nicely
coherent. This seems odd (in the sense that it works without the msync
under Linux).
The region is mmapped with:
mmap(NULL, tdb->map_size,
PROT_READ|(tdb->read_only? 0:PROT_WRITE),
MAP_SHARED|MAP_FILE, tdb->fd, 0);
What I notice is that all the calls to mmap return the same address.
A careful reading of the man pages for mmap and munmap does not suggest
that I am doing anything wrong.
Is it possible that FreeBSD is deferring flushing the dirty data, and then
forgets to do it when the same starting address is used etc?
Regards
-----
Richard Sharpe, rsharpe[at]richardsharpe.com, rsharpe[at]samba.org,
sharpe[at]ethereal.com, http://www.richardsharpe.com
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