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Re: mingw and same-inode
Re: mingw and same-inode
Thu, 24 Sep 2009 06:18:43 -0600
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According to Jim Meyering on 9/24/2009 12:29 AM:
> bool same = false;
> same = SAME_INODE (source_dir_stats, dest_dir_stats);
> if (same < 0)
> same = (identical_basenames
> && strcmp (source_basename, dest_basename) == 0);
As written, it wouldn't have worked, anyways. The idea is that "./file"
and "/path/to/file" can be the same name, so we need more than a strcmp of
the dirnames. Rather, it needs a strcmp of the canonicalized names. And
since mingw doesn't have working canonicalize_file_name yet, it probably
even means using getcwd/chdir(dirname)/getcwd/chdir(cwd) twice to
determine the two names to compare.
> Your new test, "same < 0" will never be true when
> compiled on a system with proper "bool" support.
I missed that too. All the more reason that I reverted the patch.
> Apparently, since your testing did not expose this flaw,
> no tested use of same_name requires the new semantics of SAME_INODE.
Correct - on mingw, I had tested the use of SAME_INODE, but not of
same_name (it made a difference as to whether at_func2 mistakenly assumed
two fds pointed to the same directory). Fortunately, on every other
platform, SAME_INODE is still 0 or 1 (mingw is the only platform where
st_ino is always 0, and therefore SAME_INODE was returning 1 even when it
should have returned 0, leading to the tri-state proposal in the first
place). I suppose that for mingw, I could also beef up SAME_INODE to
return 0 instead of -1 if other reliable fields in st_ino, such as st_ctim
or st_size, differ. (Note that on mingw, st_ctim is mistakenly the file
creation time, corresponding to birthtime in BSD stat, rather than the
last metadata change time as per POSIX, but it still serves as a reliable
indicator of different files).
> If the tri-state test is required in only a few places,
> how about using a new macro, say SAME_INODE_TRISTATE,
> in just those few places?
There's two categories of clients of SAME_INODE - those that want to do
something if the files are provably the same (any where I changed to
SAME_INODE()==1), but which behave correctly if the files are different or
indeterminate; and those that want to do something if the files are
provably different, but which behave correctly if the files are the same
or indeterminate. If SAME_INODE can be reached on mingw, then a decision
about what to do in the indeterminate case is necessary, even if we can
reduce the indeterminate result.
Don't work too hard, make some time for fun as well!
Eric Blake address@hidden
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