plug part of the history problems until we can do better:

do not change the underlying file when truncating; rather,
copy everything back from the tmpfile to histfd while the
latter is locked

Build.sh

@@ -1,5 +1,5 @@
 #!/bin/sh
-srcversion='$MirOS: src/bin/mksh/Build.sh,v 1.725 2017/05/15 13:35:38 tg Exp $'
+srcversion='$MirOS: src/bin/mksh/Build.sh,v 1.726 2017/08/07 20:40:56 tg Exp $'
 #-
 # Copyright (c) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
 #		2011, 2012, 2013, 2014, 2015, 2016, 2017
@@ -2090,6 +2090,11 @@ ac_test mmap lock_fcntl 0 'for mmap and munmap' <<-'EOF'
 	    munmap(NULL, 0)); }
 EOF
 
+ac_test ftruncate mmap 0 'for ftruncate' <<-'EOF'
+	#include <unistd.h>
+	int main(void) { return (ftruncate(0, 0)); }
+EOF
+
 ac_test nice <<-'EOF'
 	#include <unistd.h>
 	int main(void) { return (nice(4)); }
@@ -2244,8 +2249,8 @@ EOF
 # other checks
 #
 fd='if to use persistent history'
-ac_cache PERSISTENT_HISTORY || case $HAVE_MMAP$HAVE_FLOCK$HAVE_LOCK_FCNTL in
+ac_cache PERSISTENT_HISTORY || case $HAVE_FTRUNCATE$HAVE_MMAP$HAVE_FLOCK$HAVE_LOCK_FCNTL in
-11*|101) fv=1 ;;
+111*|1101) fv=1 ;;
 esac
 test 1 = $fv || check_categories="$check_categories no-histfile"
 ac_testdone
@@ -2404,7 +2409,7 @@ addsrcs '!' HAVE_STRLCPY strlcpy.c
 addsrcs USE_PRINTF_BUILTIN printf.c
 test 1 = "$USE_PRINTF_BUILTIN" && add_cppflags -DMKSH_PRINTF_BUILTIN
 test 1 = "$HAVE_CAN_VERB" && CFLAGS="$CFLAGS -verbose"
-add_cppflags -DMKSH_BUILD_R=551
+add_cppflags -DMKSH_BUILD_R=561
 
 $e $bi$me: Finished configuration testing, now producing output.$ao
 

histrap.c

@@ -27,7 +27,7 @@
 #include <sys/file.h>
 #endif
 
-__RCSID("$MirOS: src/bin/mksh/histrap.c,v 1.162 2017/04/29 22:04:28 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/histrap.c,v 1.163 2017/08/07 20:40:57 tg Exp $");
 
 Trap sigtraps[ksh_NSIG + 1];
 static struct sigaction Sigact_ign;
@@ -714,26 +714,65 @@ histsave(int *lnp, const char *cmd, int svmode, bool ignoredups)
 
 #if HAVE_PERSISTENT_HISTORY
 static const unsigned char sprinkle[2] = { HMAGIC1, HMAGIC2 };
-#endif
 
-void
+static int
-hist_init(Source *s)
+hist_persist_back(int srcfd)
+{
+	off_t tot, mis;
+	ssize_t n, w;
+	char *buf, *cp;
+	int rv = 0;
+#define MKSH_HS_BUFSIZ 4096
+
+	if ((buf = malloc_osfunc(MKSH_HS_BUFSIZ)) == NULL)
+		return (1);
+
+	tot = lseek(srcfd, (off_t)0, SEEK_END);
+	lseek(srcfd, (off_t)0, SEEK_SET);
+	lseek(histfd, (off_t)0, SEEK_SET);
+
+	mis = tot;
+	while (mis > 0) {
+		if ((n = blocking_read(srcfd, (cp = buf),
+		    MKSH_HS_BUFSIZ)) == -1) {
+			if (errno == EINTR) {
+				intrcheck();
+				continue;
+			}
+			goto copy_error;
+		}
+		mis -= n;
+		while (n) {
+			if (intrsig)
+				goto has_intrsig;
+			if ((w = write(histfd, cp, n)) != -1) {
+				n -= w;
+				cp += w;
+				continue;
+			}
+			if (errno == EINTR) {
+ has_intrsig:
+				intrcheck();
+				continue;
+			}
+			goto copy_error;
+		}
+	}
+	if (ftruncate(histfd, tot)) {
+ copy_error:
+		rv = 1;
+	}
+	free_osfunc(buf);
+	return (rv);
+}
+
+static void
+hist_persist_init(void)
 {
-#if HAVE_PERSISTENT_HISTORY
 	unsigned char *base;
 	int lines, fd;
-	enum { hist_init_first, hist_init_retry, hist_init_restore } hs;
+	enum { hist_init_first, hist_init_retry, hist_use_it } hs;
-#endif
 
-	histsave(NULL, NULL, HIST_DISCARD, true);
-
-	if (Flag(FTALKING) == 0)
-		return;
-
-	hstarted = true;
-	hist_source = s;
-
-#if HAVE_PERSISTENT_HISTORY
 	if (((hname = str_val(global("HISTFILE"))) == NULL) || !*hname) {
 		hname = NULL;
 		return;
@@ -753,9 +792,8 @@ hist_init(Source *s)
 	mksh_lockfd(histfd);
 
 	histfsize = lseek(histfd, (off_t)0, SEEK_END);
-	if (histfsize > MKSH_MAXHISTFSIZE || hs == hist_init_restore) {
+	if (histfsize > MKSH_MAXHISTFSIZE) {
 		/* we ignore too large files but still append to them */
-		/* we also don't need to re-read after truncation */
 		goto hist_init_tail;
 	} else if (histfsize > 2) {
 		/* we have some data, check its validity */
@@ -781,6 +819,7 @@ hist_init(Source *s)
 			if ((fd = binopen3(nhname, O_RDWR | O_CREAT | O_TRUNC |
 			    O_EXCL, 0600)) < 0) {
 				/* just don't truncate then, meh. */
+				hs = hist_use_it;
 				goto hist_trunc_dont;
 			}
 			if (fstat(histfd, &sb) >= 0 &&
@@ -795,28 +834,26 @@ hist_init(Source *s)
 			hp = history;
 			while (hp < histptr) {
 				if (!writehistline(fd,
-				    s->line - (histptr - hp), *hp))
+				    hist_source->line - (histptr - hp), *hp))
 					goto hist_trunc_abort;
 				++hp;
 			}
-			/* now unlock, close both, rename, rinse, repeat */
+			/* now transfer back */
+			if (!hist_persist_back(fd)) {
+				/* success! */
+				hs = hist_use_it;
+			}
+ hist_trunc_abort:
+			/* remove temporary file */
 			close(fd);
 			fd = -1;
-			hist_finish();
+			unlink(nhname);
-			if (rename(nhname, hname) < 0) {
+			/* use whatever is in the file now */
- hist_trunc_abort:
-				if (fd != -1)
-					close(fd);
-				unlink(nhname);
-				if (fd != -1)
-					goto hist_trunc_dont;
-				/* darn! restore histfd and pray */
-			}
-			hs = hist_init_restore;
  hist_trunc_dont:
 			afree(nhname, ATEMP);
-			if (hs == hist_init_restore)
+			if (hs == hist_use_it)
-				goto retry;
+				goto hist_trunc_done;
+			goto hist_init_fail;
 		}
 	} else if (histfsize != 0) {
 		/* negative or too small... */
@@ -840,9 +877,26 @@ hist_init(Source *s)
 			return;
 		}
 	}
+ hist_trunc_done:
 	histfsize = lseek(histfd, (off_t)0, SEEK_END);
  hist_init_tail:
 	mksh_unlkfd(histfd);
+}
+#endif
+
+void
+hist_init(Source *s)
+{
+	histsave(NULL, NULL, HIST_DISCARD, true);
+
+	if (Flag(FTALKING) == 0)
+		return;
+
+	hstarted = true;
+	hist_source = s;
+
+#if HAVE_PERSISTENT_HISTORY
+	hist_persist_init();
 #endif
 }