// vim: set noet sw=2 ts=2 sts=2:
#define _GNU_SOURCE
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/sendfile.h>
#include <string.h>
#include <stdlib.h>
#include <sys/wait.h>

typedef struct argv_t {
	char *pid;        // %p
	char *global_pid; // %P
	char *tid;        // %i
	char *global_tid; // %I
	char *uid;        // %u
	char *gid;        // %g
	char *dump_mode;  // %d
	char *signal;     // %s
	char *ts;         // %t
	char *hostname;   // %h
	char *exefn_;     // %e
	char *exefn;      // %f
	char *exepath;    // %E
	char *max_size;   // %c
	char *cpu;        // %C
} argv_t;

const char const expected_pattern[] = "|%s [-d DESTDIR] [-a EXEPATH] %%p %%P %%i %%I %%u %%g %%d %%s %%t %%h %%e %%f %%E %%c %%C";
const unsigned int const expected_argc = 15;

typedef char *path_t;

typedef struct args_t {
	path_t _self;
	path_t coredir;
	pid_t  pid;
	pid_t  global_pid;
	uint   tid;
	uint   global_tid;
	uid_t  uid;
	gid_t  gid;
	uint   dump_mode;
	uint   signal;
	uint   ts;
	char*  hostname;
	path_t exefn_;
	path_t exefn;
	path_t exepath;
	size_t max_size;
	uint   cpu;
	path_t after;
	char   corefile[1024];
} args_t;
// if max_size is 0 or bigger than MAX_SIZE, then MAX_SIZE (1GiB):
#define MAX_SIZE 1073741824

int prsint( long unsigned int *dst, char *src) {
	*dst = 0;
	for( uint i = 0; src[i]; i++) {
		if( '0' <= src[i] && src[i] <= '9')
			*dst = 10*(*dst) + src[i]-'0';
		else
			return -1;
	}
	return 0;
}
#define CHK_EXST( key) \
	if( NULL == v->key) { \
		fprintf( stderr, "ERROR: Missing value for: %s\n", #key); \
		return -1; \
	}
#define TOSTR( key) CHK_EXST( key) \
	s->key = v->key;
#define TOINT( key) CHK_EXST( key) \
	if( -1 == prsint( &b, v->key)) { \
		fprintf( stderr, "ERROR: Invalid value in: %s=%s\n", #key, v->key); \
		return -1; \
	} \
	s->key = b;

int argv2args( argv_t *v, args_t *s) {
	long unsigned int b;
	TOINT( pid);
	TOINT( global_pid);
	TOINT( tid);
	TOINT( global_tid);
	TOINT( uid);
	TOINT( gid);
	TOINT( dump_mode);
	TOINT( signal);
	TOINT( ts);
	TOSTR( hostname);
	TOSTR( exefn_);
	TOSTR( exefn);
	TOSTR( exepath);
	TOINT( max_size);
	TOINT( cpu);
}

int proc_filename( char *dest, size_t len, args_t *args, char* fn) {
	size_t destl = snprintf( dest, len, "/proc/%i/%s", args->pid, fn);
	if( destl < 0) {
		fprintf( stderr, "ERROR: gen path for %s: %s (%i)\n", fn, strerror( errno), errno);
		return 1;
	}
	if( len <= destl) {
		fprintf( stderr, "ERROR: gen path for %s: /proc/-path to long: destl=%lu\n", fn, destl);
		return 1;
	}
	return 0;
}

int core_filename( char *dest, size_t len, args_t *args, char* ext) {
	size_t destl = snprintf( dest, len, "%s/core%s.%u", args->coredir, ext, args->pid);
	if( destl < 0) {
		fprintf( stderr, "ERROR: gen path for core%s: %s (%i)\n", ext, strerror( errno), errno);
		return 1;
	}
	if( len <= destl) {
		fprintf( stderr, "ERROR: gen path for core%s: /proc/-path to long: destl=%lu\n", ext, destl);
		return 1;
	}
	return 0;
}

void show_opened_files() {
	pid_t selfpid = getpid();
	pid_t child = fork();
	switch( child) {
	case -1:
		fprintf( stderr, "ERROR: error while forking: %s (%i)\n", strerror( errno), errno);
		break;
	case 0:
		char dir[1024];
		snprintf( dir, sizeof dir, "/proc/%i/fd/", selfpid);
		execl( "/usr/bin/env", "env", "ls", "-la", dir, NULL);
		fprintf( stderr, "ERROR: Executing ls failed: %s (%i)\n", strerror( errno), errno);
		exit( 2);
	default:
		int ws;
		waitpid( child, &ws, 0);
	}
}

int dump_core( args_t *args) {
	// Concept: Once used, not necessary anymore, we cen reuse the space again.
	int wfd; // write file handler.
	struct stat stat; // Needed for determine size of file.

	// copy stdin -> core.pid
	if( core_filename( args->corefile, sizeof args->corefile, args, ""))
		return 1;
	if( -1 == (wfd = open( args->corefile, O_WRONLY | O_CREAT | O_TRUNC, 0600))) {
		fprintf( stderr, "ERROR: Cannot open file %s: %s (%i)\n", args->corefile, strerror( errno), errno);
		return 1;
	}
	if( -1 == splice(
			STDIN_FILENO, 0,
			wfd, 0,
			(args->max_size || MAX_SIZE < args->max_size) ? args->max_size : MAX_SIZE, 0)) {
		fprintf( stderr, "ERROR: Cannot write core to file %s: %s (%i)\n", args->corefile, strerror( errno), errno);
		return 1;
	}
	close( wfd);
	return 0;
}

int copy_fd_to_fd( int infd, int outfd) {
	char buf[1024];
	size_t left;
	while( 0 < (left = read( infd, buf, sizeof buf))) {
		char *wb = buf;
		ssize_t wr;
		while( left > (wr = write( outfd, wb, left))) {
			if( -1 == wr) {
				return -1;
			}
			left -= wr;
		}
	}
}

int dump_cmdline( args_t *args) {
	// Concept: Once used, not necessary anymore, we cen reuse the space again.
	char path[1024]; // For any paths.
	int rfd; // read file handler.
	int wfd; // write file handler.
	struct stat stat; // Needed for determine size of file.

	// copy /proc/pid/cmdline -> core-cmdline.pid
	if( proc_filename( path, sizeof path, args, "cmdline")) return 1;
	if( -1 == (rfd = open( path, O_RDONLY, 0644))) {
		fprintf( stderr, "ERROR: Cannot open file %s: %s (%i)\n", path, strerror( errno), errno);
		return 1;
	}
	if( -1 == fstat( rfd, &stat)) {
		fprintf( stderr, "ERROR: Cannot stat of file %s: %s (%i)\n", path, strerror( errno), errno);
		return 1;
	}
	if( core_filename( path, sizeof path, args, "-cmdline")) return 1;
	if( -1 == (wfd = open( path, O_WRONLY | O_CREAT | O_TRUNC, 0644))) {
		fprintf( stderr, "ERROR: Cannot open file %s: %s (%i)\n", path, strerror( errno), errno);
		return 1;
	}
	//show_opened_files();
	//if( -1 == sendfile( wfd, rfd, NULL, 1024*1024)) {
	if( -1 == copy_fd_to_fd( rfd, wfd)) {
		fprintf( stderr, "ERROR: Cannot write to file %s: %s (%i)\n", path, strerror( errno), errno);
		return 1;
	}
	close( rfd);
	close( wfd);

	return 0;
}

#define P( s, m) if( -1 == fprintf( wfh, "%s=%s\n", #s, argv->m)) { \
		fprintf( stderr, "ERROR: Cannot write to file %s: %s (%i)\n", path, strerror( errno), errno); \
		return 1; \
	}
int dump_md( argv_t *argv, args_t *args) {
	// Concept: Once used, not necessary anymore, we cen reuse the space again.
	char path[1024]; // For any paths.
	FILE *wfh;

	// write argv -> core-md.pid
	if( core_filename( path, sizeof path, args, "-md")) return 1;
	umask( 0133);
	if( NULL == (wfh = fopen( path, "w"))) {
		fprintf( stderr, "ERROR: Cannot open file %s: %s (%i)\n", path, strerror( errno), errno);
		return 1;
	}
	P(p, pid)
	P(P, global_pid)
	P(i, tid)
	P(I, global_tid)
	P(u, uid)
	P(g, gid)
	P(d, dump_mode)
	P(s, signal)
	P(t, ts)
	P(h, hostname)
	P(e, exefn_)
	P(f, exefn)
	P(E, exepath)
	P(c, max_size)
	P(C, cpu)
	fclose( wfh);

	return 0;
}

int usage( args_t *args) {
	fprintf( stderr, "Usage in kernel.core_pattern=\"");
	fprintf( stderr, expected_pattern, args->_self);
	fprintf( stderr, "\"\n");
	if( '/' != args->_self[0])
		fprintf( stderr, "\tAttention: Absolut path instead of %s should be used!\n", args->_self);
	fprintf( stderr, "\n  -a EXEPATH\tExecutes EXEPATH after dumping core as child process, before itself exits.\n");
	fprintf( stderr, "\t\tAs arguments, the path to core-file will be provided.\n");
	fprintf( stderr, "  -d DESTDIR\tDestination directory for core-files and additional files. (default: /var/cores)\n");
	exit(2);
}

void run_after( args_t *args) {
	if( args->after) {
		pid_t child = fork();
		switch( child) {
		case -1:
			fprintf( stderr, "ERROR: error while forking: %s (%i)\n", strerror( errno), errno);
			break;
		case 0:
			execl( args->after, args->after, args->corefile, NULL);
			fprintf( stderr, "ERROR: Executing after-program failed: %s (%i)\n", strerror( errno), errno);
			exit( 2);
		}
	}
}

void parse_args( size_t argc, char** _argv, argv_t **argv, args_t *args) {
	args->after   = NULL;
	args->coredir = "/var/cores";
	args->_self   = realpath( _argv[0], NULL);

	char opt;
	while( -1 != (opt = getopt( argc, _argv, "hd:a:"))) {
		switch( opt) {
		case 'h': usage( args); break;
		case 'a': args->after   = optarg; break;
		case 'd': args->coredir = optarg; break;
		default:
			fprintf( stderr, "ERROR: Unknown option: -%c\n", opt);
			usage( args);
		}
	}

	if( expected_argc > argc-optind+1) {
		fprintf( stderr, "ERROR: %u arguments expected. Given: %li\n", expected_argc, argc-optind+1);
		usage( args);
		exit(2);
	}

	*argv = (argv_t*) (_argv + optind);
	argv2args( *argv, args);
}

int main( size_t argc, char **_argv) {
	argv_t *argv = malloc( sizeof (argv_t));
	args_t *args = malloc( sizeof (args_t));
	parse_args( argc, _argv, &argv, args);

	//fprintf( stderr, "dump core...\n");
	dump_core( args);
	// That's all, core dump written. :)
	// But, hold on, now the funny things will follow, which are the differences to a simple core-dump.

	//fprintf( stderr, "dump cmdline...\n");
	dump_cmdline( args);
	//fprintf( stderr, "dump metadata...\n");
	dump_md( argv, args);

	//fprintf( stderr, "run after program...\n");
	run_after( args);

	//fprintf( stderr, "exit...\n");
	return 0;
}