main/xen: remove perl dependency

use a tiny C program to do the file/fd compare instead of perl

1 files changed, 62 insertions, 0 deletions

diff --git a/main/xen/xen-fd-is-file.c b/main/xen/xen-fd-is-file.c
new file mode 100644
index 0000000000..a1518e4df0
--- /dev/null
+++ b/main/xen/xen-fd-is-file.c
@@ -0,0 +1,62 @@
+#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);
+}