dj.1: clarify skip/seek behavior with regards to statistics output

Makefile

@@ -16,9 +16,12 @@
 DESTDIR ?= dist
 PREFIX ?= /usr/local
 
-MANDIR != [ $(PREFIX) = / ] && printf '/usr/share/man\n' \
+# normalized prefix
+PREFIX_N != (test -d $(PREFIX) && [ '-' != $(PREFIX) ] \
+	&& CDPATH= cd -P -- $(PREFIX) && pwd -P)
+MANDIR != [ $(PREFIX_N) = / ] && printf '/usr/share/man\n' \
 	|| printf '/share/man\n'
-SYSEXITS != printf '\043include <sysexits.h>\n' | cpp -M - | sed 's/ /\n/g' \
+SYSEXITS != printf '\043include <sysexits.h>\n' | cpp -M - | tr ' ' '\n' \
 	| sed -n 's/sysexits\.h//p' || printf 'include\n'
 
 CC ?= cc
@@ -29,7 +32,7 @@ RUSTLIBS = --extern getopt=build/o/libgetopt.rlib \
 CFLAGS += -I$(SYSEXITS)
 
 .PHONY: all
-all: docs dj false fop hru intcmp mm npc rpn scrut str strcmp swab true
+all: dj false fop hru intcmp mm npc rpn scrut str strcmp swab true
 
 # keep build/include until bindgen(1) has stdin support
 # https://github.com/rust-lang/rust-bindgen/issues/2703
@@ -40,8 +43,8 @@ build:
 clean:
 	rm -rf build dist
 
-dist: all
-	mkdir -p $(DESTDIR)/$(PREFIX)/bin $(DESTDIR)/$(PREFIX)/share/man/man1
+dist: all docs
+	mkdir -p $(DESTDIR)/$(PREFIX)/bin $(DESTDIR)/$(PREFIX)/$(MANDIR)/man1
 	cp build/bin/* $(DESTDIR)/$(PREFIX)/bin
 	cp build/docs/*.1 $(DESTDIR)/$(PREFIX)/$(MANDIR)/man1
 

docs/dj.1

@@ -4,14 +4,14 @@
 .\" This work is licensed under CC BY-SA 4.0. To see a copy of this license,
 .\" visit <http://creativecommons.org/licenses/by-sa/4.0/>.
 .\"
-.TH DJ 1 2024-06-17 "Harakit X.X.X"
+.TH DJ 1 2024-06-29 "Harakit X.X.X"
 .SH NAME
 dj \(en disk jockey
 .\"
 .SH SYNOPSIS
 
 dj
-.RB [ -AdHnq ]
+.RB [ -Hn ]
 .RB [ -a\ byte ]
 .RB [ -c\ count ]
 
@@ -35,7 +35,9 @@ respectively. This language is inherited from the
 utility and used here to decrease ambiguity.
 
 When seeking or skipping to a byte, writing or reading starts at the byte
-immediately subsequent to the specified byte.
+immediately subsequent to the specified byte. Seeks and skips aren\(cqt counted
+in the output statistics because they're guaranteed to succeed (or the utility
+will exit unsuccessfully).
 .\"
 .SH OPTIONS
 
@@ -44,58 +46,46 @@ Takes a file path as an argument and opens it for use as an input.
 .IP \fB-b\fP\ \fIblock_size\fP
 Takes a numeric argument as the size in bytes of the input buffer, the default
 being 1024.
-.IP \fB-s\fP\ \fIoffset\fP
-Takes a numeric argument as the number of bytes to skip into the input
-before starting to read. If the standard input is used, bytes read to this point
-are discarded.
-.IP \fB-o\fP\ \fIfile\fP
+.IP \fB-s\fP
+Takes a numeric argument as the index of the byte at which reading will
+commence; \(lqskips\(rq that number of bytes. If the standard input is used,
+bytes read to this point are discarded.
+.IP \fB-o\fP
 Takes a file path as an argument and opens it for use as an output.
 .IP \fB-B\fP\ \fIblock_size\fP
 Does the same as
 .B -b
 but for the output buffer.
-.IP \fB-S\fP\ \fIoffset\fP
-Seeks a number of bytes through the output before starting to write from
-the input. If the output is a stream, null characters are printed.
-.IP \fB-a\fP\ \fIbyte\fP
+.IP \fB-S\fP
+Takes a numeric argument as the index of the byte at which writing will
+commence; \(lqseeks\(rq that number of bytes. If the standard output is used,
+null characters are printed.
+.IP \fB-a\fP
 Accepts a single literal byte with which the input buffer is padded in the event
-of an incomplete read from the input file.
-.IP \fB-A\fP
-Specifying this option pads the input buffer with null bytes in the event of an
-incomplete read. This is equivalent to specifying
-.B -a
-with a null byte instead of a character.
-.IP \fB-c\fP\ \fIcount\fP
+of an incomplete read from the input file. If the option argument is empty, the
+null byte is used.
+.IP \fB-c\fP
 Specifies a number of reads to make. The default is 0, in which case the
 input is read until a partial or empty read is made.
-.IP \fB-d\fP
-Prints invocation information before program execution as described in the
-DIAGNOSTICS section. Each invocation increments the debug level of the
-program.
 .IP \fB-H\fP
-Prints diagnostics messages in a human-readable manner as described in the
+Prints diagnostic messages in a human-readable manner as described in the
 DIAGNOSTICS section.
 .IP \fB-n\fP
 Retries failed reads once before exiting.
-.IP \fB-q\fP
-Suppresses error messages which print when a read or write is partial or
-empty. Each invocation decrements the debug level of the program.
 .\"
 .SH STANDARD INPUT
 
 The standard input shall be used as an input if no inputs are specified or if
-one or more of the input files is \(lq-\(rq.
+input file is \(lq-\(rq.
 .\"
 .SH STANDARD OUTPUT
 The standard output shall be used as an output if no inputs are specified or if
-one or more of the input files is \(lq-\(rq.
+the output file is \(lq-\(rq.
 .\"
 .SH DIAGNOSTICS
 
-On a partial or empty read, unless the
-.B -q
-option is specified, a diagnostic message is printed. Then, the program exits
-unless the
+On a partial or empty read, a diagnostic message is printed. Then, the program
+exits unless the
 .B -n
 option is specified.
 
@@ -120,20 +110,6 @@ option may be specified. In this event, the following format is used instead:
 {ASCII line feed}
 .RE
 
-If the
-.B -d
-option is specified, debug information will be printed at the beginning of
-execution. This output contains information regarding how the program was
-invoked. The following example is the result of running the program with
-.B -d
-as the only argument:
-
-.RS
-argv0=dj
-in=<stdin>      ibs=1024        skip=0  align=ff       count=0
-out=<stdout>    obs=1024        seek=0  debug= 3       noerror=0
-.RE
-
 In non-recoverable errors that don\(cqt pertain to the read-write cycle, a
 diagnostic message is printed and the program exits with the appropriate
 .BR sysexits.h (3)
@@ -148,9 +124,7 @@ is specified along with the
 option and a count, actual byte output is the product of the count and the input
 block size and therefore may be lower than expected. If the
 .B -a
-or
-.B -A
-options are specified, this could make written data nonsensical.
+option is specified, this could make written data nonsensical.
 .\"
 .SH CAVEATS
 

src/dj.c

@@ -16,17 +16,21 @@
  * along with this program. If not, see https://www.gnu.org/licenses/.
  */
 
-#include <ctype.h> /* isupper(3), tolower(3) */
+#include <assert.h> /* assert(3) */
 #include <errno.h> /* errno */
 #include <fcntl.h> /* open(2) */
 #include <stdio.h> /* fprintf(3), stderr */
-#include <stdlib.h> /* free(3), malloc(3), strtol(3), size_t */
+#include <stdlib.h> /* malloc(3), strtol(3), size_t */
 #include <string.h> /* memcpy(3), memmove(3), memset(3) */
 #include <sysexits.h> /* EX_OK, EX_USAGE */
 #include <unistd.h> /* close(2), getopt(3), lseek(2), read(2), write(2),
                      * optarg, optind, STDIN_FILENO, STDOUT_FILENO */
+#include <sys/stat.h> /* S_IRGRP, S_IROTH, S_IRUSR, S_IWGRP, S_IWOTH,
+                         S_IWUSR */
 extern int errno;
 
+char *program_name = "dj";
+
 /* dj uses two structures that respectively correspond to the reading and
  * writing ends of its jockeyed "pipe". User-configurable members are noted
  * with their relevant options. */
@@ -41,95 +45,30 @@ struct Io{
 	int prec;		/* partial records processed */
 	int rec;		/* records processed */
 	long seek;		/* bytes to seek/skip (will be 0 after skippage) (-sS) */
-} ep[2]; /* "engineered pipe"; also "extended play", for the deejay */
+}; 
 
-/* Additionally, the following global variables are used to store user options.
- */
+/* To be assigned to main:fmt and used with printio(). */
+static char *fmt_asv   = "%d\037%d\036%d\037%d\035%d\036%d\034";
+static char *fmt_human = "%d+%d > %d+%d; %d > %d\n";
 
-/* (-a)  */ static int align; /* Only the lower 8b are used but align is
-                               * negative if no alignment is being done. */
-
-/* (-c)  */ static int count; /* 0 if dj(1) runs until no more reads are
-                               * possible. */
-
-/* ASCII field separator delimited statistics */
-            static char *fmt_asv   = "%d\037%d\036%d\037%d\035%d\036%d\034";
-/* human-readable statistics */
-            static char *fmt_human = "%d+%d > %d+%d; %d > %d\n";
-/* pointer to chosen formatting */
-/* (-H)  */ static char *fmt_output; /* fmt_asv (default) or fmt_human (-H) */
-
-/* (-dq) */ static char debug;       /*
- *  -d  increments             dj -qq | 0 - no diagnostic output whatsoever
- *   -q decrements             dj -q  | 1 - typical output without
- *                                    |     notifications on partial reads or
- *                                    |     writes
- *                             dj     | 2 - typical output (default)
- *                             dj -d  | 3 - verbose status messages */
-
-/* (-n)  */ static char noerror;     /* 0 - exits on partial reads or writes
-                                      *     (default)
-                                      * 1 - retries on partial reads/writes
-                                      *     (-n) */
-
-/* Non-configurable defaults. */
-#define bs_default 1024 /* GNU dd(1) default; twice POSIX but a neat 2^10 */
-static char *program_name = "<no argv[0]>";
 static char *stdin_name = "<stdin>";
 static char *stdout_name = "<stdout>";
-static int read_flags = O_RDONLY; /* These flags are consistent with Busybox */
-static int write_flags = O_WRONLY | O_CREAT; /* dd(1). */
 
-/* Macro to set defaults for user-configurable options. */
-#define setdefaults do{ \
-	align = -1; \
-	count = 0; \
-	debug = 2; \
-	fmt_output = fmt_asv; \
-	noerror = 0; \
-	ep[0].fl = read_flags; \
-	Io_setdefaults(&ep[0]); \
-	ep[1].fl = write_flags; \
-	Io_setdefaults(&ep[1]); }while(0)
+static int read_flags = O_RDONLY; /* Consistent with Busybox dd(1). */
+static int write_flags = O_WRONLY | O_CREAT;
 
 #define MIN(a, b) (((a) < (b)) ? (a) : (b))
 
-/* Macro to check if fd is a std* file, e.g. stdin. */
-#define fdisstd(fd) \
-		((fd) == STDIN_FILENO \
-		|| (fd) == STDOUT_FILENO \
-		|| (fd) == STDERR_FILENO)
-
-/* Macro to call the cleanup functions that operate on struct io on the
- * particular io[2] used in main. Error conditions are not checked because this
- * is only used when the program is about to terminate (hence its name). */
-#define terminate(io) do{ \
-	Io_buffree(&(io)[0]); \
-	Io_buffree(&(io)[1]); \
-	Io_fdclose(&(io)[0]); \
-	Io_fdclose(&(io)[1]); }while(0)
-
-/* Allocates *io's buffer. Returns NULL if unsuccessful. */
-static void *
-Io_bufalloc(struct Io *io){
-
-	return (io->buf = malloc(io->bs * (sizeof *io->buf)));
-}
-
-/* Frees *io's buffer. Returns io. */
-static struct Io *
-Io_buffree(struct Io *io){
-
-	free(io->buf);
-
-	return io;
-}
+/* Macro to check if fd is stdin or stdout */
+#define fdisstd(fd) ((fd) == STDIN_FILENO || (fd) == STDOUT_FILENO)
 
 /* Fills the unused portion of io's buffer with padding, updating io->bufuse.
  * Returns io. */
 static struct Io *
 Io_bufrpad(struct Io *io, int padding){
-	
+
+	assert(io != NULL);
+
 	memset(io->buf + io->bufuse, padding, io->bs - io->bufuse);
 	io->bufuse = io->bs;
 
@@ -144,6 +83,8 @@ static struct Io*
 Io_bufxapp(struct Io *dest, struct Io *src){
 	int n;
 
+	assert(dest != NULL && src != NULL);
+
 	n = MIN(src->bufuse, dest->bs - dest->bufuse);
 	memcpy(dest->buf + dest->bufuse, src->buf, n);
 	dest->bufuse += n;
@@ -160,32 +101,27 @@ Io_bufxapp(struct Io *dest, struct Io *src){
 static struct Io*
 Io_bufxfer(struct Io *dest, struct Io *src, int n){
 
+	assert(dest != NULL && src != NULL);
+
 	memcpy(dest->buf, src->buf, (dest->bufuse = n));
 	memmove(src->buf, src->buf + n, (src->bufuse -= n));
 
 	return dest;
 }
 
-/* Closes io->fn and returns -1 on error, otherwise io->fd. */
-static int
-Io_fdclose(struct Io *io){
-
-	return fdisstd(io->fd)
-		? 0
-		: close(io->fd);
-}
-
 /* Opens io->fn and saves the file descriptor into io->fd. Returns io->fd,
  * which will be -1 if an error occured. */
 static int
 Io_fdopen(struct Io *io, char *fn){
 	int fd;
-	
+
+	assert(io != NULL);
+
 	if((fd = open(fn, io->fl,
 					/* these are the flags used by touch(1p) */
 					S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH))
 				!= -1
-			&& Io_fdclose(io) == 0){
+			&& (fdisstd(io->fd) || close(io->fd) == 0)){
 		io->fd = fd;
 		io->fn = fn;
 	}
@@ -193,44 +129,6 @@ Io_fdopen(struct Io *io, char *fn){
 	return fd;
 }
 
-/* Seeks io->seek bytes through *io's file descriptor, (counter-intuitively)
- * returning -1 if successful and a sysexits.h exit code if an unrecoverable
- * error occurred. io->buf will be cleared of useful bytes and io->seek will
- * be set to zero to indicate the seek occurred. */
-static int
-Io_fdseek(struct Io *io){
-	int (*op)(int, void *, size_t);
-	
-	if(!fdisstd(io->fd) && lseek(io->fd, io->seek, SEEK_SET) != -1)
-		return -1;
-
-	/* repeated code to get the condition out of the loop */
-	if(io->fl == write_flags){
-		memset(io->buf, '\0', io->bs);
-		/* We're going to cheat and use bufuse as the retval for write(2),
-		 * which is fine because it'll be zeroed as this function returns
-		 * anyway. */
-		do{
-			if((io->bufuse = write(io->fd, io->buf, MIN(io->bs, io->seek)))
-					== 0)
-				/* second chance */
-				io->bufuse = write(io->fd, io->buf, MIN(io->bs, io->seek));
-		}while((io->seek -= io->bufuse) > 0 && io->bufuse != 0);
-	}else if(io->fl == read_flags){
-		do{
-			if((io->bufuse = read(io->fd, io->buf, MIN(io->bs, io->seek)))
-					== 0)
-				/* second chance */
-				io->bufuse = read(io->fd, io->buf, MIN(io->bs, io->seek));
-		}while((io->seek -= io->bufuse) > 0 && io->bufuse != 0);
-	}else
-		return EX_SOFTWARE;
-
-	io->bufuse = 0;
-
-	return -1;
-}
-
 /* Reads io->bs bytes from *io's file descriptor into io->buf, storing the
  * number of read bytes in io->bufuse and updating io->bytes. If io->bufuse is
  * 0, errno will probably be set. Returns io. */
@@ -242,23 +140,6 @@ Io_read(struct Io *io){
 	return io;
 }
 
-/* Sets the variables in a struct *io to the defaults. Identifies the read/
- * write ends of the "pipe" by checking io->fl. Returns io. */
-static struct Io *
-Io_setdefaults(struct Io *io){
-
-	io->bs = bs_default;
-	io->buf = NULL;
-	io->bytes = 0;
-	io->fd = (io->fl == read_flags) ? STDIN_FILENO : STDOUT_FILENO;
-	io->fn = (io->fl == read_flags) ? stdin_name   : stdout_name;
-	io->prec = 0;
-	io->rec = 0;
-	io->seek = 0;
-
-	return io;
-}
-
 /* Writes io->bufuse units from io->buf to io->fd, permuting any unwritten
  * bytes to the start of io->buf and updating io->bufuse. If io->bufuse doesn't
  * change, errno will probably be set. Returns io. */
@@ -284,14 +165,13 @@ oserr(char *s){
 }
 
 /* Prints statistics regarding the use of dj, particularly partially and
- * completely read and written records, accessing debug, ep, and fmt_output. */
+ * completely read and written records. */
 static void
-output(void){
+printio(char *fmt, struct Io io[2]){
 
-	if(debug >= 1)
-		fprintf(stderr, fmt_output,
-			ep[0].rec, ep[0].prec, ep[1].rec, ep[1].prec,
-			ep[0].bytes, ep[1].bytes);
+	fprintf(stderr, fmt,
+		io[0].rec, io[0].prec, io[1].rec, io[1].prec,
+		io[0].bytes, io[1].bytes);
 
 	return;
 }
@@ -311,9 +191,9 @@ parse(char *s){
 }
 
 static int
-usage(void){
+usage(char *s){
 
-	fprintf(stderr, "Usage: %s [-AdfHqQ] [-a byte] [-c count]\n"
+	fprintf(stderr, "Usage: %s [-Hn] [-a byte] [-c count]\n"
 		"\t[-i file] [-b block_size] [-s offset]\n"
 		"\t[-o file] [-B block_size] [-S offset]\n",
 		program_name);
@@ -322,131 +202,169 @@ usage(void){
 }
 
 int main(int argc, char *argv[]){
-	int c;
-	int i;
+	int align; /* low 8b used, negative if no alignment is being done */
+	int count; /* 0 if dj(1) runs until no more reads are possible */
+	char *fmt; /* == fmt_asv (default) or fmt_human (-H) */
+	size_t i; /* side of io being modified */
+	struct Io io[2];
+	char noerror; /* 0=exits (default) 1=retries on partial reads or writes */
 
-	setdefaults;
+	/* Set defaults. */
+	align = -1;
+	count = 0;
+	fmt = fmt_asv;
+	noerror = 0;
+	for(i = 0; i < 2; ++i){
+		io[i].bs = 1024 /* 1 KiB */; /* GNU dd(1) default; POSIX says 512B */
+		io[i].bytes = 0;
+		io[i].fd = i == 0 ? STDIN_FILENO : STDOUT_FILENO;
+		io[i].fn = i == 0 ? stdin_name   : stdout_name;
+		io[i].fl = i == 0 ? read_flags   : write_flags;
+		io[i].prec = 0;
+		io[i].rec = 0;
+		io[i].seek = 0;
+	}
 
 	if(argc > 0){
+		int c;
+
 		program_name = argv[0];
-		while((c = getopt(argc, argv, "a:Ab:B:c:di:hHnqs:S:o:")) != -1)
+		while((c = getopt(argc, argv, ":a:b:B:c:i:hHns:S:o:")) != -1)
 			switch(c){
-			case 'i': case 'o':
-				i = (c == 'o');
+			case 'i': case 'o': i = (c == 'o');
 				if(optarg[0] == '-' && optarg[1] == '\0'){ /* optarg == "-" */
-					ep[i].fd = (i == 0) ? STDIN_FILENO : STDOUT_FILENO;
-					ep[i].fn = (i == 0) ? stdin_name   : stdout_name;
+					io[i].fd = i == 0 ? STDIN_FILENO : STDOUT_FILENO;
+					io[i].fn = i == 0 ? stdin_name   : stdout_name;
 					break;
-				}else if(Io_fdopen(&ep[i], optarg) != -1)
+				}else if(Io_fdopen(&io[i], optarg) != -1)
 					break;
-				terminate(ep);
 				return oserr(optarg);
-			case 'A': align = '\0'; break;
-			case 'd': ++debug; break;
 			case 'n': noerror = 1; break;
-			case 'H': fmt_output = fmt_human; break;
-			case 'q': --debug; break;
+			case 'H': fmt = fmt_human; break;
 			case 'a':
-				if(optarg[0] != '\0' && optarg[1] == '\0'){
+				if(optarg[0] == '\0' || optarg[1] == '\0'){
 					align = optarg[0];
 					break;
 				}
 				/* FALLTHROUGH */
-			case 'c': case 'b': case 's': case 'B': case 'S':
+			case 'c': case 'b': case 's': case 'B': case 'S': /* numbers */
 				if(c == 'c' && (count = parse(optarg)) >= 0)
 					break;
-				i = isupper(c);
-				c = tolower(c);
-				if((c == 'b' && (ep[i].bs = parse(optarg)) > 0)
-						|| (c == 's' && (ep[i].seek = parse(optarg)) >= 0))
+				i = (c >= 'A' && c <= 'Z');
+				c |= 0x20 /* 0b 0010 0000 */; /* (ASCII) make lowercase */
+				if((c == 'b' && (io[i].bs = parse(optarg)) > 0)
+						|| (c == 's' && (io[i].seek = parse(optarg)) >= 0))
 					break;
 				/* FALLTHROUGH */
 			default:
-				terminate(ep);
-				return usage();
+				return usage(program_name);
 			}
 	}
 
-	if(debug >= 3)
-		fprintf(stderr,
-			"argv0=%s\n"
-			"in=%s\tibs=%d\tskip=%ld\talign=%hhx\tcount=%d\n"
-			"out=%s\tobs=%d\tseek=%ld\tdebug=%2d\tnoerror=%d\n",
-			program_name,
-			ep[0].fn, ep[0].bs, ep[0].seek, align, count,
-			ep[1].fn, ep[1].bs, ep[1].seek, debug, noerror);
+	assert(io->fd != STDIN_FILENO  || io->fl == read_flags);
+	assert(io->fd != STDOUT_FILENO || io->fl == write_flags);
 
 	if(argc > optind){
-		terminate(ep);
-		return usage();
+		return usage(program_name);
 	}
 
-	for(i = 0; i <= 1; ++i){
-		if(Io_bufalloc(&ep[i]) == NULL){
+	for(i = 0; i < 2; ++i){
+		/* buffer allocation */
+		if((io[i].buf = malloc(io[i].bs * (sizeof *(io[i].buf)))) == NULL){
 			fprintf(stderr, "%s: Failed to allocate %d bytes\n",
-				program_name, ep[i].bs);
-			terminate(ep);
+				program_name, io[i].bs);
 			return EX_OSERR;
-		}else if(ep[i].seek > 0)
-			switch(Io_fdseek(&ep[i])){
-			case EX_OK:
-				output();
-				terminate(ep);
-				return EX_OK;
-			}
+		}
+		/* easy seeking */
+		if(!fdisstd(io[i].fd) && lseek(io[i].fd, io[i].seek, SEEK_SET) != -1)
+			io[i].seek = 0;
 	}
 
+	/* hard skipping */
+	if(io[0].seek > 0){
+		do{
+			if((io[0].bufuse = read(
+						io[0].fd, io[0].buf, MIN(io[0].bs, io[0].seek)))
+					== 0)
+				/* second chance */
+				io->bufuse = read(
+					io[0].fd, io[0].buf, MIN(io[0].bs, io[0].seek));
+		}while((io[0].seek -= io[0].bufuse) > 0 && io[0].bufuse != 0);
+		io[0].bufuse = 0;
+	}
+
+	/* hard seeking */
+	if(io[1].seek > 0){
+		memset(io[1].buf, '\0', io[1].bs);
+		/* We're going to cheat and use bufuse as the retval for write(2),
+		 * which is fine because it'll be zeroed as this function returns
+		 * anyway. */
+		do{
+			if((io[1].bufuse = write(
+						io[1].fd, io[1].buf, MIN(io[1].bs, io[1].seek)))
+					== 0)
+				/* second chance */
+				io[1].bufuse = write(
+					io[1].fd, io[1].buf, MIN(io[1].bs, io[1].seek));
+		}while((io[1].seek -= io[1].bufuse) > 0 && io[1].bufuse != 0);
+		io[1].bufuse = 0;
+	}
+
+	/* Sought bytes aren't counted in the statistics because successful seeking
+	 * is guaranteed here. */
+	for(i = 0; i < 2; ++i)
+		if(io[i].seek > 0)
+			return oserr(io[i].fn);
+
 	do{	/* read */
-		Io_read(&ep[0]);
-		if(!noerror && ep[0].bufuse == 0)
-			Io_read(&ep[0]); /* second chance */
-		if(ep[0].bufuse == 0) /* that's all she wrote */
+		Io_read(&io[0]);
+		if(!noerror && io[0].bufuse == 0)
+			Io_read(&io[0]); /* second chance */
+		if(io[0].bufuse == 0) /* that's all she wrote */
 			break;
-		else if(ep[0].bufuse < ep[0].bs){
-			++ep[0].prec;
-			if(debug >= 2){
-				fprintf(stderr, "%s: Partial read:\n\t", program_name);
-				output();
-			}
+		else if(io[0].bufuse < io[0].bs){
+			++io[0].prec;
+			fprintf(stderr, "%s: Partial read:\n\t", program_name);
+			printio(fmt, io);
 			if(!noerror)
 				count = 1;
 			if(align >= 0)
-				Io_bufrpad(&ep[0], align);
+				Io_bufrpad(&io[0], align);
 		}else
-			++ep[0].rec;
+			++io[0].rec;
 
 		/* write */
-		do{	if(ep[1].bs > ep[0].bs){ /* io[1].bs > io[0].bs */
-				Io_bufxapp(&ep[1], &ep[0]);
-				if(ep[0].bs + ep[1].bufuse <= ep[1].bs && count != 1)
+		do{
+			int t;
+
+			if(io[1].bs > io[0].bs){
+				Io_bufxapp(&io[1], &io[0]);
+				if(io[0].bs + io[1].bufuse <= io[1].bs && count != 1)
 					continue; /* we could write more */
 			}else
-				Io_bufxfer(&ep[1], &ep[0], MIN(ep[0].bufuse, ep[1].bs));
+				Io_bufxfer(&io[1], &io[0], MIN(io[0].bufuse, io[1].bs));
 
-			c = ep[1].bufuse;
-			Io_write(&ep[1]);
-			if(!noerror && ep[1].bufuse == c)
-				Io_write(&ep[1]); /* second chance */
-			if(c == ep[1].bufuse){ /* no more love */
+			t = io[1].bufuse;
+			Io_write(&io[1]);
+			if(!noerror && io[1].bufuse == t)
+				Io_write(&io[1]); /* second chance */
+			if(t == io[1].bufuse){ /* no more love */
 				count = 1;
 				break;
-			}else if(c > ep[1].bufuse && ep[1].bufuse > 0){
-				ep[1].prec += 1;
-				if(debug >= 2){
-					fprintf(stderr, "%s: Partial write:\n\t", program_name);
-					output();
-				}
+			}else if(t > io[1].bufuse && io[1].bufuse > 0){
+				io[1].prec += 1;
+				fprintf(stderr, "%s: Partial write:\n\t", program_name);
+				printio(fmt, io);
 				if(!noerror)
 					count = 1;
-			}else if(ep[1].bufuse == 0 && c < ep[1].bs)
-				++ep[1].prec;
+			}else if(io[1].bufuse == 0 && t < io[1].bs)
+				++io[1].prec;
 			else
-				++ep[1].rec;
-		}while(ep[0].bufuse > 0);
+				++io[1].rec;
+		}while(io[0].bufuse > 0);
 	}while(count == 0 || --count > 0);
 
-	output();
-	terminate(ep);
+	printio(fmt, io);
 
 	return EX_OK;
 }