mkswap

Andries.Brouwer@cwi.nl
Thu, 19 Feb 1998 22:22:32 +0100 (MET)

I just noticed that I can do
mkswap foo; swapon foo
which fails, ("Unable to find swap-space signature"), while
mkswap foo; sync; swapon foo
succeeds. In other words (2.0.33): the swapon system call
does not look at the cache for the file foo.
This is a kernel bug (but there are more aliasing problems
somewhat like this, like between /dev/hda and /dev/hda1).

I patched mkswap.c, adding a sync:

--- mkswap.c~ Sun Jul 6 02:11:03 1997
+++ mkswap.c Thu Feb 19 21:49:40 1998
@@ -223,5 +223,11 @@
die("unable to rewind swap-device");
if (PAGE_SIZE != write(DEV, signature_page, PAGE_SIZE))
die("unable to write signature page");
+ /*
+ * A subsequent swapon() will fail if the signature
+ * is not actually on disk. (This is a kernel bug.)
+ */
+ if (fsync(DEV))
+ die("fsync failed");
return 0;
}

Andries

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