Also I should add, I've yet to find a way to protect a file from
editing or deletion on OS X that can't just be ignored by something
else. Things like flock appear to be optionally supported and not
globally enforced. As long as a way exists to get around any kind of
file lock there's no way to guarantee a specific file will be
unchanged during usage. This is partially done to prevent file lock
abuse I'm guessing.
As Mr. Davidson pointed out, the best you can do is only map files you
can be reasonably sure no one will want to modify unless purposely
trying to corrupt your program.
On May 13, 2008, at 9:57 PM, Michael Vannorsdel wrote:
I actually tested this a month back and not all operations/programs
respect link counts nor does the system appear to enforce them. For
instance an rm -f will destroy the file regardless of link count, as
well as some obscure APIs. After the file was removed the mapping
program crashed when trying to read more of the file; it failed to
load new map data.
On May 13, 2008, at 9:08 AM, Jens Alfke wrote:
You're correct about modifications, but not about deletions. An
open file descriptor counts as a link to a file, so the unlink(2)
system call will not actually delete the file from disk because
there's still a link to it. Once you close the mapped file, the
last link goes away and then the file is actually deleted.
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