1. Built in glibc 2.28 and gcc 8.2.0:

  mkfifo/fopen/fread/fwrite kind of worked with glibc 2.26 and gcc 7.2.0.
  With 2.28 named-pipe reading with fread would read the pipe only once for
  some reason - probably because it stopped being a 'blocking' call
  To fix - switched to open/read/poll combination - so none of glibc functions
  is used.

2. camogm_fifo_reader - test program - use with *_writer or just 'echo'
3. camogm_fifo_writer - test program

src/Makefile

 GUIDIR     = camogmgui
 PROGS      = camogm
 TEST_PROG  = camogm_test 
+TEST_PROG1  = camogm_fifo_writer
+TEST_PROG2  = camogm_fifo_reader
+ 
 PHPSCRIPTS = camogmstate.php $(GUIDIR)/camogmgui.php $(GUIDIR)/camogmgui.css $(GUIDIR)/camogmgui.js $(GUIDIR)/camogm_interface.php \
              $(GUIDIR)/SpryTabbedPanels.css $(GUIDIR)/SpryTabbedPanels.js $(GUIDIR)/xml_simple.php $(GUIDIR)/SpryCollapsiblePanel.css \
              $(GUIDIR)/SpryCollapsiblePanel.js
@@ -13,6 +16,9 @@ IMAGES     = $(GUIDIR)/images/filebrowser-01.gif $(GUIDIR)/images/filebrowser-bo
 
 SRCS = camogm.c camogm_ogm.c camogm_jpeg.c camogm_mov.c camogm_kml.c camogm_read.c index_list.c camogm_align.c
 TEST_SRC = camogm_test.c 
+TEST_SRC1 = camogm_fifo_writer.c 
+TEST_SRC2 = camogm_fifo_reader.c
+
 OBJS = $(SRCS:.c=.o)
 
 CFLAGS    += -Wall -I$(STAGING_DIR_HOST)/usr/include-uapi
@@ -28,17 +34,21 @@ BINDIR     = /usr/bin/
 WWW_PAGES  = /www/pages
 IMAGEDIR   = $(WWW_PAGES)/images
 
-all: $(PROGS) $(TEST_PROG)
+all: $(PROGS) $(TEST_PROG) $(TEST_PROG1) $(TEST_PROG2)
 
 $(PROGS): $(OBJS)
 	$(CC) $(CFLAGS) $(LDFLAGS) $^ $(LDLIBS) -o $@
 
 $(TEST_PROG): $(TEST_SRC:.c=.o) 
+$(TEST_PROG1): $(TEST_SRC1:.c=.o)
+$(TEST_PROG2): $(TEST_SRC2:.c=.o)
 
 install: $(PROGS) $(PHPSCRIPTS) $(CONFIGS)
 	$(INSTALL) $(OWN) -d $(DESTDIR)$(BINDIR)
 	$(INSTALL) $(OWN) -m $(INSTMODE) $(PROGS)      $(DESTDIR)$(BINDIR)
 	$(INSTALL) $(OWN) -m $(INSTMODE) $(TEST_PROG)  $(DESTDIR)$(BINDIR)
+	$(INSTALL) $(OWN) -m $(INSTMODE) $(TEST_PROG1)  $(DESTDIR)$(BINDIR)
+	$(INSTALL) $(OWN) -m $(INSTMODE) $(TEST_PROG2)  $(DESTDIR)$(BINDIR)
 	$(INSTALL) $(OWN) -d $(DESTDIR)$(SYSCONFDIR)
 	$(INSTALL) $(OWN) -m $(INSTDOCS) $(CONFIGS)    $(DESTDIR)$(SYSCONFDIR)
 	$(INSTALL) $(OWN) -d $(DESTDIR)$(WWW_PAGES)

src/camogm.c

@@ -30,6 +30,8 @@
 #include <ctype.h>
 #include <elphel/ahci_cmd.h>
 
+#include <poll.h>
+
 #include "camogm_ogm.h"
 #include "camogm_jpeg.h"
 #include "camogm_mov.h"
@@ -38,6 +40,8 @@
 
 /** @brief Default debug level */
 #define DEFAULT_DEBUG_LVL         6
+/** @brief Default poll() timeout in ms*/
+#define DEFAULT_POLL_TIMEOUT      1000
 /** @brief JPEG trailer size in bytes */
 #define TRAILER_SIZE              0x02
 /** @brief Default segment duration in seconds */
@@ -1301,7 +1305,9 @@ char * getLineFromPipe(FILE* npipe)
 	if (!cmdbufp) cmdbuf[cmdbufp] = 0;  //null-terminate first access (probably not needed for the static buffer
 	nlp = strpbrk(cmdbuf, ";\n");
 	if (!nlp) { //no complete string, try to read more
-		fl = fread(&cmdbuf[cmdbufp], 1, sizeof(cmdbuf) - cmdbufp - 1, npipe);
+		// 2019/01/16: this change is related to switching to poll()
+		//fl = fread(&cmdbuf[cmdbufp], 1, sizeof(cmdbuf) - cmdbufp - 1, npipe);
+		fl = read(npipe, &cmdbuf[cmdbufp], sizeof(cmdbuf) - cmdbufp - 1);
 		cmdbuf[cmdbufp + fl] = 0;
 // is there any complete string in a buffer after reading?
 		nlp = strpbrk(&cmdbuf[cmdbufp], ";\n"); // there were no new lines before cmdbufp
@@ -1548,6 +1554,8 @@ int listener_loop(camogm_state *state)
 	int curr_port = 0;
 	const char *pipe_name = state->pipe_name;
 
+	struct pollfd pfd;
+
 	// create a named pipe
 	// always delete the pipe if it existed, start a fresh one
 	f_ok = access(pipe_name, F_OK);
@@ -1567,6 +1575,8 @@ int listener_loop(camogm_state *state)
 		}
 	}
 
+	/* old */
+	/*
 	// now open the pipe - will block until something will be written (or just open for writing,
 	// reads themselves will not block)
 	if (!((cmd_file = fopen(pipe_name, "r")))) {
@@ -1574,6 +1584,27 @@ int listener_loop(camogm_state *state)
 		clean_up(state);
 		return -5;
 	}
+	*/
+
+	/* new: 2019/01/16 */
+
+	// Adding poll() because supposedly read calls (read, fread)
+	// stopped being blocking at all
+
+	// Why O_RDWR?
+	// https://stackoverflow.com/questions/22021253/poll-on-named-pipe-returns-with-pollhup-constantly-and-immediately
+
+	if (!((cmd_file = open(pipe_name, O_RDWR|O_NONBLOCK)))) {
+		D0(fprintf(debug_file, "Can not open command file %s\n", pipe_name));
+		clean_up(state);
+		return -5;
+	}
+	/* force(?) disable O_NONBLOCK */
+	fcntl(cmd_file, F_SETFL, 0);
+	// ready to read
+	pfd.events = POLLIN;
+	pfd.fd     = cmd_file;
+
 	D0(fprintf(debug_file, "Pipe %s open for reading\n", pipe_name)); // to make sure something is sent out
 
 	// enter main processing loop
@@ -1581,6 +1612,14 @@ int listener_loop(camogm_state *state)
 		curr_port = select_port(state);
 		state->port_num = curr_port;
 		// look at command queue first
+
+		ret = poll(&pfd,1,DEFAULT_POLL_TIMEOUT);
+
+		if (ret==0){
+			D6(fprintf(debug_file, "Waiting for commands...\n"));
+		}
+
+		if (pfd.revents & POLLIN){
 			cmd = parse_cmd(state, cmd_file);
 			if (cmd) {
 				if (cmd < 0) D0(fprintf(debug_file, "Unrecognized command\n"));
@@ -1674,6 +1713,7 @@ int listener_loop(camogm_state *state)
 				state->rawdev.thread_state = STATE_RUNNING;
 				usleep(COMMAND_LOOP_DELAY);     // make it longer but interruptible by signals?
 			}
+		} // if pfd.revents & POLLIN
 	} // while (process)
 
 	// normally, we should not be here

src/camogm_fifo_reader.c

+/** @brief This define is needed to use lseek64 and should be set before includes */
+#define _LARGEFILE64_SOURCE
+/** Needed for O_DIRECT */
+#define _GNU_SOURCE
+
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <errno.h>
+#include <stdbool.h>
+
+#include <fcntl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <linux/fs.h>
+#include <ctype.h>
+#include <sys/uio.h>
+
+#include <poll.h>
+
+// set to 1 second
+#define CAMOGM_TIMEOUT 1000
+
+int main(int argc, char *argv[]){
+
+	int f_ok;
+	int ret;
+	int fer, feo;
+	long int ftl;
+	int i=0;
+	const char pipe_name[] = "/tmp/fifo_test";
+	int flags;
+
+	char cmdbuf[1024];
+	int fl;
+
+	int somecounter = 0;
+	int writecounter = 0;
+
+	FILE *cmd_file;
+
+	struct pollfd pfd;
+	pfd.events = POLLIN;
+
+	printf("This is reader. It creates FIFO: %s\n",pipe_name);
+
+	// always delete pipe if it exists
+	f_ok = access(pipe_name, F_OK);
+	ret = unlink(pipe_name);
+
+	if (ret && f_ok == 0) {
+		printf("Some error\n");
+	}
+
+	ret = mkfifo(pipe_name, 0666); //EEXIST
+	if (ret) {
+		if (errno==EEXIST){
+			printf("Pipe exists\n");
+		}
+	}
+
+	cmd_file = open(pipe_name, O_RDWR|O_NONBLOCK);
+	pfd.fd = cmd_file;
+	fcntl(cmd_file, F_SETFL, 0);  /* disable O_NONBLOCK */
+
+	printf("Pipe is now open for reading\n");
+
+	while(true){
+
+		ret = poll(&pfd, 1, CAMOGM_TIMEOUT);  /* poll to avoid reading EOF */
+		somecounter +=1;
+
+		if (ret==0) {
+			printf("TIMEOUT %d\n",somecounter);
+		}
+
+		if (pfd.revents & POLLIN){
+
+			printf("PostPoll %d %d, revents = %d,  errno = %d\n",somecounter,ret,pfd.revents,errno);
+
+			fl = read(cmd_file, cmdbuf, sizeof(cmdbuf));
+			//clearerr(cmd_file);
+
+			if (fl>0) {
+				writecounter +=1;
+			}
+
+			if (fl<0) {
+				printf("Error?\n");
+				break;
+			}
+
+
+			//fl = read(cmd_file,cmdbuf,sizeof(cmdbuf));
+			if ((fl>10)||(somecounter>10000000)) {
+				break;
+			}
+		}
+	}
+
+	printf("EXIT! errno=%d writes=%d wdc=%d\n",errno,writecounter,somecounter);
+
+	return 0;
+}

src/camogm_fifo_writer.c

+/** @brief This define is needed to use lseek64 and should be set before includes */
+#define _LARGEFILE64_SOURCE
+/** Needed for O_DIRECT */
+#define _GNU_SOURCE
+
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <errno.h>
+#include <stdbool.h>
+
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <linux/fs.h>
+#include <ctype.h>
+#include <sys/uio.h>
+
+int main(int argc, char *argv[]){
+
+	FILE *cmd_file;
+	const char pipe_name[] = "/tmp/fifo_test";
+	const char message[]   = "test";
+	int ret;
+
+	printf("This is writer\n");
+
+	cmd_file = fopen(pipe_name, "w");
+
+	while(true){
+		ret = fwrite(message,sizeof(char),sizeof(message),cmd_file);
+		printf("Wrote %d bytes, fwrite returned %d\n",sizeof(message),ret);
+	}
+
+	return 0;
+}

src/camogm_read.c

@@ -1017,8 +1017,8 @@ void *reader(void *arg)
 			.sockfd_const = &sockfd,
 			.sockfd_temp = &fd
 	};
-	memset(&index_dir, 0, sizeof(struct disk_index));
-	memset(&index_sparse, 0, sizeof(struct disk_index));
+	memset(&index_dir, 0, sizeof(struct disk_idir));
+	memset(&index_sparse, 0, sizeof(struct disk_idir));
 
 	prep_socket(&sockfd, state->sock_port);
 	pthread_cleanup_push(exit_thread, &exit_state);