Re: Unable to read history on latest Cygwin

[Peter Stephenson <pws@xxxxxxx>]

On Mon, 14 Dec 2009 15:19:29 +0100
"Thorsten Kampe" <thorsten@xxxxxxxxxxxxxxxx> wrote:
> the new Cygwin 1.7 release is soon to be released. According to Cygwin 
> Project Co-Leader Corinna Vinschen, Cygwin will drop "fake support" for 
> emulating hardlinks on FAT32: "Hardlinks on FAT [...] have been faked in 
> 1.5 by copying the file. The decision was made a couple of weeks back to 
> drop this fake since the application should know that the underlying 
> filesystem is not capable of creating hardlinks."
> 
> The result of that is that I'm not able to run zsh "portable" from a 
> FAT32 USB thumb drive: "zsh: failed to create hard link as lock file 
> /home/thorsten/.zhistory.LOCK: operation not permitted". (Zsh is running 
> but history is neither saved nor written). histfcntllock also results in 
> errors.
> 
> "Your best bet now might be to report this as an upstream bug to zsh, 
> and recommend that they use an alternative approach, such as symlink 
> locking (the way emacs does things), if hard link locking doesn't work 
> because of the underlying file system."

I presume that means symlink() works OK?  We should probably be able to do
something relatively straightforward like the following---using exactly the
same code for symbolic links as hard links, most of the change is indenting
code---though I've only checked it to the extent that it doesn't screw up
somewhere that does support hard links.

I haven't dared check specifically for EPERM, although in theory I could.

> Bash does not exihibit the error.

I don't see the relevance.  Have you any reason to suppose it would and
that this would affect zsh?  There are various ways of simulating file
locking.

Index: configure.ac
===================================================================
RCS file: /cvsroot/zsh/zsh/configure.ac,v
retrieving revision 1.128
diff -u -r1.128 configure.ac
--- configure.ac	29 Sep 2009 19:19:21 -0000	1.128
+++ configure.ac	14 Dec 2009 15:10:55 -0000
@@ -1169,7 +1169,8 @@
 	       htons ntohs \
 	       regcomp regexec regerror regfree \
 	       gdbm_open getxattr \
-	       realpath canonicalize_file_name)
+	       realpath canonicalize_file_name \
+	       symlink)
 AC_FUNC_STRCOLL
 
 if test x$enable_cap = xyes; then
Index: Src/hist.c
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/hist.c,v
retrieving revision 1.95
diff -u -r1.95 hist.c
--- Src/hist.c	16 Aug 2009 20:37:45 -0000	1.95
+++ Src/hist.c	14 Dec 2009 15:10:55 -0000
@@ -2601,40 +2601,59 @@
 	char *lockfile;
 #ifdef HAVE_LINK
 	char *tmpfile;
+	int failed = 0;
 #endif
 
 	lockfile = bicat(unmeta(fn), ".LOCK");
 #ifdef HAVE_LINK
-	if ((fd = gettempfile(fn, 0, &tmpfile)) >= 0) {
-	    FILE *out = fdopen(fd, "w");
-	    if (out) {
-		fprintf(out, "%ld %s\n", (long)getpid(), getsparam("HOST"));
-		fclose(out);
-	    } else
-		close(fd);
-	    while (link(tmpfile, lockfile) < 0) {
-		if (errno != EEXIST)
-		    zerr("failed to create hard link as lock file %s: %e",
-			 lockfile, errno);
-		else if (!keep_trying)
-		    ;
-		else if (stat(lockfile, &sb) < 0) {
-		    if (errno == ENOENT)
+#ifdef HAVE_SYMLINK
+	do
+#endif
+	{
+	    if ((fd = gettempfile(fn, 0, &tmpfile)) >= 0) {
+		FILE *out = fdopen(fd, "w");
+		if (out) {
+		    fprintf(out, "%ld %s\n", (long)getpid(), getsparam("HOST"));
+		    fclose(out);
+		} else
+		    close(fd);
+		while (
+#ifdef HAVE_SYMLINK
+		    (failed ? symlink(tmpfile, lockfile) :
+		     link(tmpfile, lockfile)) < 0
+#else
+		    link(tmpfile, lockfile) < 0
+#endif
+		    ) {
+		    if (errno != EEXIST)
+			failed++; /* could check for EPERM here */
+		    else if (!keep_trying)
+			;
+		    else if (stat(lockfile, &sb) < 0) {
+			if (errno == ENOENT)
+			    continue;
+			zerr("failed to stat lock file %s: %e",
+			     lockfile, errno);
+		    } else {
+			if (time(NULL) - sb.st_mtime < 10)
+			    sleep(1);
+			else
+			    unlink(lockfile);
 			continue;
-		    zerr("failed to stat lock file %s: %e", lockfile, errno);
-		} else {
-		    if (time(NULL) - sb.st_mtime < 10)
-			sleep(1);
-		    else
-			unlink(lockfile);
-		    continue;
+		    }
+		    lockhistct--;
+		    break;
 		}
-		lockhistct--;
-		break;
+		unlink(tmpfile);
+		free(tmpfile);
 	    }
-	    unlink(tmpfile);
-	    free(tmpfile);
 	}
+#ifdef HAVE_SYMLINK
+	while (failed == 1);
+#endif
+	if (failed)
+	    zerr("failed to create link as lock file %s: %e",
+		 lockfile, errno);
 #else /* not HAVE_LINK */
 	while ((fd = open(lockfile, O_WRONLY|O_CREAT|O_EXCL, 0644)) < 0) {
 	    if (errno != EEXIST || !keep_trying)

-- 
Peter Stephenson <pws@xxxxxxx>            Software Engineer
Tel: +44 (0)1223 692070                   Cambridge Silicon Radio Limited
Churchill House, Cambridge Business Park, Cowley Road, Cambridge, CB4 0WZ, UK


Member of the CSR plc group of companies. CSR plc registered in England and Wales, registered number 4187346, registered office Churchill House, Cambridge Business Park, Cowley Road, Cambridge, CB4 0WZ, United Kingdom