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#include <sys/stat.h>
#include <stdio.h>
#include <fcntl.h>
#include <err.h>
/*
this is to be used as:
while true; do
eval "exec $_lockfd<>$_lockfile"
flock -x $_lockfd || return $?
if xen-fd-is-file $_lockfd $_lockfile; then break; fi
eval "exec $_lockfd<&-"
done
instead of:
local rightfile
while true; do
eval "exec $_lockfd<>$_lockfile"
flock -x $_lockfd || return $?
# We can't just stat /dev/stdin or /proc/self/fd/$_lockfd or
# use bash's test -ef because those all go through what is
# actually a synthetic symlink in /proc and we aren't
# guaranteed that our stat(2) won't lose the race with an
# rm(1) between reading the synthetic link and traversing the
# file system to find the inum. Perl is very fast so use that.
rightfile=$( perl -e '
open STDIN, "<&'$_lockfd'" or die $!;
my $fd_inum = (stat STDIN)[1]; die $! unless defined $fd_inum;
my $file_inum = (stat $ARGV[0])[1];
print "y\n" if $fd_inum eq $file_inum;
' "$_lockfile" )
if [ x$rightfile = xy ]; then break; fi
# Some versions of bash appear to be buggy if the same
# $_lockfile is opened repeatedly. Close the current fd here.
eval "exec $_lockfd<&-"
done
*/
int main(int argc, char *argv[])
{
int lockfd;
const char *filename;
struct stat fdst, filest;
if (argc <= 2)
errx(1, "usage: %s FDNUM FILENAME\n", argv[0]);
lockfd = atoi(argv[1]);
filename = argv[2];
if (fstat(lockfd, &fdst) < 0)
err(2, "fstat(%i)", lockfd);
if (stat(filename, &filest) < 0)
err(3, "stat(%s)", filename);
return (fdst.st_ino != filest.st_ino);
}
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