Use interruptible iopen() to open input file.

Opening the read side of a fifo blocks until someone opens the write
side. SIGINT doesn't interrupt that block because less catches SIGINT.
Use new function iopen() to open the file; iopen can be interrupted
by intio() which is called from the signal handler.

This makes SIGINT work correctly, but SIGTSTP doesn't yet work as
expected: it doesn't stop the process, it just aborts the iopen like SIGINT.

configure.ac

@@ -215,7 +215,9 @@ AH_TEMPLATE([HAVE_FILENO],
 AH_TEMPLATE([HAVE_ERRNO],
 	[Define HAVE_ERRNO if you have the errno variable.])
 AH_TEMPLATE([MUST_DEFINE_ERRNO],
-	[Define MUST_DEFINE_ERRNO if you have errno but it is not define in errno.h.])
+	[Define MUST_DEFINE_ERRNO if you have errno but it is not defined in errno.h.])
+AH_TEMPLATE([HAVE_SETTABLE_ERRNO],
+	[Define HAVE_SETTABLE_ERRNO if the errno variable can be assigned to.])
 AH_TEMPLATE([HAVE_SYS_ERRLIST],
 	[Define HAVE_SYS_ERRLIST if you have the sys_errlist[] variable.])
 AH_TEMPLATE([HAVE_OSPEED],
@@ -320,6 +322,17 @@ AC_LINK_IFELSE([AC_LANG_PROGRAM([[
 #endif]], [[extern int errno; static int x; x = errno;]])],[AC_MSG_RESULT(yes - must define); AC_DEFINE(HAVE_ERRNO) AC_DEFINE(MUST_DEFINE_ERRNO)],[AC_MSG_RESULT(no)])
 fi
 
+have_settable_errno=no
+if test $have_errno = yes; then
+AC_MSG_CHECKING(for settable errno)
+AC_LINK_IFELSE([AC_LANG_PROGRAM([[
+#if HAVE_ERRNO_H
+#include <errno.h>
+#else
+extern int errno;
+#endif]], [[errno = 0;]])],[AC_MSG_RESULT(yes); AC_DEFINE(HAVE_SETTABLE_ERRNO)],[])
+fi
+
 AC_MSG_CHECKING(for locale)
 AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <locale.h>
 #include <ctype.h>

defines.ds

@@ -278,6 +278,7 @@
 #define HAVE_ERRNO 1
 #define MUST_DEFINE_ERRNO 1
 #endif
+#define HAVE_SETTABLE_ERRNO 1
 
 /* Define HAVE_SYS_ERRLIST if you have the sys_errlist[] variable */
 #define HAVE_SYS_ERRLIST 1

defines.o2

@@ -245,10 +245,11 @@
 #define HAVE_FILENO 1
 
 /* Define HAVE_ERRNO if you have the errno variable */
-/* Define MUST_DEFINE_ERRNO if you have errno but it is not define 
- * in errno.h */
 #define HAVE_ERRNO 1
+/* Define MUST_DEFINE_ERRNO if you have errno but it is not defined in errno.h */
 /* #undef MUST_DEFINE_ERRNO */
+/* Define HAVE_SETTABLE_ERRNO if the errno variable can be assigned to. */
+#define HAVE_SETTABLE_ERRNO 1
 
 /* Define HAVE_SYS_ERRLIST if you have the sys_errlist[] variable */
 #define HAVE_SYS_ERRLIST 1

defines.o9

@@ -256,10 +256,11 @@
 #define HAVE_FILENO 1
 
 /* Define HAVE_ERRNO if you have the errno variable */
-/* Define MUST_DEFINE_ERRNO if you have errno but it is not define 
- * in errno.h */
 #define HAVE_ERRNO 1
+/* Define MUST_DEFINE_ERRNO if you have errno but it is not defined in errno.h */
 #define MUST_DEFINE_ERRNO 0
+/* Define HAVE_SETTABLE_ERRNO if the errno variable can be assigned to. */
+#define HAVE_SETTABLE_ERRNO 1
 
 /* Define HAVE_SYS_ERRLIST if you have the sys_errlist[] variable */
 #define HAVE_SYS_ERRLIST 0

defines.wn

@@ -263,10 +263,11 @@
 #define HAVE_FILENO 1
 
 /* Define HAVE_ERRNO if you have the errno variable */
-/* Define MUST_DEFINE_ERRNO if you have errno but it is not define 
- * in errno.h */
 #define HAVE_ERRNO 1
+/* Define MUST_DEFINE_ERRNO if you have errno but it is not defined in errno.h */
 #define MUST_DEFINE_ERRNO 0
+/* Define HAVE_SETTABLE_ERRNO if the errno variable can be assigned to. */
+#define HAVE_SETTABLE_ERRNO 1
 
 /* Define HAVE_SYS_ERRLIST if you have the sys_errlist[] variable */
 #define HAVE_SYS_ERRLIST 1

edit.c

@@ -531,7 +531,7 @@ public int edit_ifile(IFILE ifile)
 				error("%s", &parg);
 				free(p);
 				return edit_error(filename, alt_filename, altpipe, ifile);
-			} else if ((f = open(open_filename, OPEN_READ)) < 0)
+			} else if ((f = iopen(open_filename, OPEN_READ)) < 0)
 			{
 				/*
 				 * Got an error trying to open it.

os.c

@@ -32,6 +32,9 @@
 #if HAVE_ERRNO_H
 #include <errno.h>
 #endif
+#if MUST_DEFINE_ERRNO
+extern int errno;
+#endif
 #if HAVE_VALUES_H
 #include <values.h>
 #endif
@@ -66,13 +69,15 @@ static lbool any_data = FALSE;
 #define LONG_JUMP       longjmp
 #endif
 
-public int reading;
+static lbool reading;
+static lbool opening;
 public lbool waiting_for_data;
 public int consecutive_nulls = 0;
 
 /* Milliseconds to wait for data before displaying "waiting for data" message. */
 static int waiting_for_data_delay = 4000;
 static jmp_buf read_label;
+static jmp_buf open_label;
 
 extern int sigs;
 extern int ignore_eoi;
@@ -163,7 +168,7 @@ public int supports_ctrl_x(void)
 
 /*
  * Like read() system call, but is deliberately interruptible.
- * A call to intread() from a signal handler will interrupt
+ * A call to intio() from a signal handler will interrupt
  * any pending iread().
  */
 public ssize_t iread(int fd, unsigned char *buf, size_t len)
@@ -190,7 +195,7 @@ public ssize_t iread(int fd, unsigned char *buf, size_t len)
 	if (!reading && SET_JUMP(read_label))
 	{
 		/*
-		 * We jumped here from intread.
+		 * We jumped here from intio.
 		 */
 		reading = FALSE;
 #if HAVE_SIGPROCMASK
@@ -292,9 +297,6 @@ public ssize_t iread(int fd, unsigned char *buf, size_t len)
 		/*
 		 * Certain values of errno indicate we should just retry the read.
 		 */
-#if MUST_DEFINE_ERRNO
-		extern int errno;
-#endif
 #ifdef EINTR
 		if (errno == EINTR)
 			goto start;
@@ -314,11 +316,41 @@ public ssize_t iread(int fd, unsigned char *buf, size_t len)
 }
 
 /*
- * Interrupt a pending iread().
+ * Like open() system call, but is interruptible.
  */
-public void intread(void)
+public int iopen(constant char *filename, int flags)
 {
-	LONG_JUMP(read_label, 1);
+	int r;
+	if (!opening && SET_JUMP(open_label))
+	{
+		opening = FALSE;
+		sigs = 0;
+#if HAVE_SETTABLE_ERRNO
+#ifdef EINTR
+		errno = EINTR;
+#endif
+#endif
+		return -1;
+	}
+	opening = TRUE;
+	r = open(filename, flags);
+	opening = FALSE;
+	return r;
+}
+
+/*
+ * Interrupt a pending iopen() or iread().
+ */
+public void intio(void)
+{
+	if (opening)
+	{
+		LONG_JUMP(open_label, 1);
+	}
+	if (reading)
+	{
+		LONG_JUMP(read_label, 1);
+	}
 }
 
 /*
@@ -363,9 +395,6 @@ public char * errno_message(constant char *filename)
 	char *m;
 	size_t len;
 #if HAVE_ERRNO
-#if MUST_DEFINE_ERRNO
-	extern int errno;
-#endif
 	p = strerror(errno);
 #else
 	p = "cannot open";

signal.c

@@ -1,3 +1,4 @@
+#include <errno.h>
 /*
  * Copyright (C) 1984-2024  Mark Nudelman
  *
@@ -15,7 +16,7 @@
  * At some convenient time, the mainline code checks to see if any
  * signals need processing by calling psignal().
  * If we happen to be reading from a file [in iread()] at the time
- * the signal is received, we call intread to interrupt the iread.
+ * the signal is received, we call intio to interrupt the iread.
  */
 
 #include "less.h"
@@ -29,7 +30,6 @@ public int sigs;
 extern int sc_width, sc_height;
 extern int linenums;
 extern int wscroll;
-extern int reading;
 extern int quit_on_intr;
 extern long jump_sline_fraction;
 
@@ -59,8 +59,7 @@ static RETSIGTYPE u_interrupt(int type)
 #if HILITE_SEARCH
 	set_filter_pattern(NULL, 0);
 #endif
-	if (reading)
-		intread(); /* May longjmp */
+	intio();
 }
 #endif
 
@@ -74,8 +73,7 @@ static RETSIGTYPE stop(int type)
 	(void) type;
 	LSIGNAL(SIGTSTP, stop);
 	sigs |= S_STOP;
-	if (reading)
-		intread();
+	intio();
 }
 #endif
 
@@ -107,8 +105,7 @@ public RETSIGTYPE winch(int type)
 		return;
 #endif
 	sigs |= S_WINCH;
-	if (reading)
-		intread();
+	intio();
 }
 #endif
 
@@ -153,8 +150,7 @@ static void sigusr(constant char *var)
 	if (isnullenv(cmd))
 		return;
 	ungetsc(cmd);
-	if (reading)
-		intread();
+	intio();
 }
 
 static RETSIGTYPE sigusr1(int type)