--- /dev/null
+.\" -*-nroff-*-
+.de VS
+.sp 1
+.RS
+.nf
+.ft B
+..
+.de VE
+.ft R
+.fi
+.RE
+.sp 1
+..
+.de hP
+.IP
+.ft B
+\h'-\w'\\$1\ 'u'\\$1\ \c
+.ft P
+..
+.ie t .ds o \(bu
+.el .ds o o
+.TH mdup 3 "4 January" "Straylight/Edgeware" "mLib utilities library"
+.SH NAME
+mdup \- renumber file descriptors
+.SH SYNOPSIS
+.B "#include <mLib/mdup.h>"
+
+.BI "int mdup(mdup_fd *" v ", size_t " n ");"
+.SH DESCRIPTION
+The
+.B mdup
+function renumbers file descriptors, using the
+.BR dup (2)
+and
+.BR dup2 (2)
+system calls. Its arguments are a pointer
+.I v
+to a vector of
+.B mdup_fd
+structures, and the length
+.I n
+of this vector, in elements. The
+.B mdup_fd
+structure is defined as
+.VS
+typedef struct mdup_fd {
+ int cur;
+ int want;
+} mdup_fd;
+.VE
+Each `slot' (element) in the vector
+.I v
+represents a file. The slot's
+.B cur
+member names the current file descriptor for this file; the
+.B want
+member is the file descriptor to move it to. In order to keep a file
+alive when you don't care which descriptor it ends up with, set
+.I want
+= \-1. Several slots may specify the same
+.B cur
+descriptor; but they all have to declare different
+.BR want s
+(except that several slots may have
+.I want
+= \-1.
+.PP
+On successful exit, the function will have rearranged the file
+descriptors as requested. To reflect this, the
+.B cur
+members will all be set to match the
+.B want
+members (except where the latter are \-1).
+.PP
+If there is a failure, then some rearrangement may have been performed
+and some not; the
+.B cur
+members are set to reflect which file descriptors are to be used.
+.PP
+The old file descriptors are
+.IR closed .
+This is different from usual
+.BR dup (2)
+behaviour, of course, but essential for reliable error handling. If you
+want to keep a particular source file descriptor open as well as make a
+new copy then specify two slots with the same
+.BR cur ,
+one with
+.B want " = " cur
+and one with the desired output descriptor.
+.PP
+The
+.B mdup
+function is capable of arbitrary file descriptor remappings. In
+particular, it works correctly even if the desired remappings contain
+cycles.
+.SS "Background: the problem that mdup solves"
+The
+.B mdup
+function is intended to be used to adjust file descriptors prior to
+invoking one of the
+.B exec
+system calls. The standard use of
+.BR dup (2)
+to establish the child process's standard input/output/error files is
+prone to errors in the case where the newly opened file in fact already
+has one of the relevant file descriptors.
+.PP
+Consider the case where we want to run a process with separate pipes
+attached to each of the standard descriptors. Typical code looks like
+this.
+.VS
+#define P_INIT { \-1, \-1 }
+int p_in[2] = P_INIT, p_out[2] = P_INIT, p_err[2] = P_INIT;
+pid_t kid = -1;
+int i;
+
+if (pipe(p_in) || pipe(p_out) || pipe(p_err)) goto error;
+if ((kid = fork()) < 0) goto error;
+if (!kid) {
+ if (dup2(p_in[0], STDIN_FILENO) < 0 ||
+ dup2(p_out[1], STDOUT_FILENO) < 0 ||
+ dup2(p_err[2], STDERR_FILENO) < 0 ||
+ close(p_in[0]) || close(p_out[0]) || close(p_err[0]) ||
+ close(p_in[1]) || close(p_out[1]) || close(p_err[1]))
+ _exit(127);
+ execvp("/bin/sh", "sh", "-c", "...", (char *)0);
+}
+\&...
+.VE
+Now suppose that, in the parent process, the standard input, output and
+error descriptors are all initially closed. After the calls to
+.BR pipe (2),
+descriptors 0, 1, and 2 refer to
+.BR p_in[0] ,
+.BR p_in[1] ,
+and
+.B p_out[0]
+respectively. In the child process, the calls to
+.BR dup2 (2)
+rearrange these. But then the
+.BR close (2)
+calls will immediately close all three descriptors, before
+.BR exec ing
+the child.
+.PP
+Here's how to rewrite the above function using
+.BR mdup .
+.VS
+#define P_INIT { \-1, \-1 }
+int p_in[2] = P_INIT, p_out[2] = P_INIT, p_err[2] = P_INIT;
+pid_t kid = -1;
+mdup_fd md[3];
+int i;
+
+if (pipe(p_in) || pipe(p_out) || pipe(p_err)) goto error;
+if ((kid = fork()) < 0) goto error;
+if (!kid) {
+ if (close(p_in[1] || close(p_out[0]) || close(p_err[0]))
+ goto _exit(127);
+ md[0].cur = p_in[0]; md[0].want = STDIN_FILENO;
+ md[1].cur = p_out[1]; md[1].want = STDOUT_FILENO;
+ md[2].cur = p_err[1]; md[2].want = STDERR_FILENO;
+ if (mdup(md, 3)) _exit(127);
+ execvp("/bin/sh", "sh", "-c", "...", (char *)0);
+}
+\&...
+.VE
+One can see that, not only is the resulting program more correct, it's
+also simpler. Note that we close the unwanted ends of the pipes
+.I before
+invoking
+.BR mdup .
+Closing them afterwards risks interfering with the newly assigned
+descriptors which are meant to be passed to the child process. Note
+also that
+.B mdup
+has taken responsibility for closing the other descriptors for the
+wanted ends of the pipes.
+.SH "SEE ALSO"
+.BR dup (2),
+.BR dup2 (2),
+.BR mLib (3).
+.SH AUTHOR
+Mark Wooding, <mdw@distorted.org.uk>
+
--- /dev/null
+/* -*-c-*-
+ *
+ * Duplicate multiple files
+ *
+ * (c) 2008 Straylight/Edgeware
+ */
+
+/*----- Licensing notice --------------------------------------------------*
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#include <errno.h>
+#include <stdlib.h>
+
+#include <unistd.h>
+
+#include "mdup.h"
+
+/*----- Data structures ---------------------------------------------------*/
+
+typedef struct mdup_fdinfo {
+
+ mdup_fd *f;
+ /* Each @fdinfo@ structure refers to one of the caller's @fd@ structures.
+ * This is it.
+ */
+
+ struct mdup_fdinfo *eqnext, *eqprev;
+ /* The caller's request list can contain more than one entry with any given
+ * @cur@ descriptor. We group them together into an equivalence class,
+ * which is doubly linked using these fields.
+ */
+
+ struct mdup_fdinfo *up;
+ /* We require that there be at most one node with any given @want@
+ * descriptor (other than @-1@). There is therefore at most one node whose
+ * @want@ is equal to my @cur@. If such a node exists, @up@ points to it;
+ * otherwise @up@ is null.
+ */
+
+ struct mdup_fdinfo *down;
+ /* Obviously, @down@ links in the opposite direction from @up@. However,
+ * there may be several nodes whose @cur@ equals my @want@; therefore
+ * @down@ simply links to one of the nodes in the equivalence class.
+ *
+ * Unsurprisingly, @down@ is the direction we move during the depth-first
+ * traversal phase of the operation.
+ */
+
+ struct mdup_fdinfo *dlink;
+ /* Nodes with @want == -1@, and nodes where we've broken cycles, are
+ * considered `dynamic': their @cur@ has been chosen by @dup@ to be
+ * distinct from any existing descriptor, but may collide with a @want@.
+ * We check each proposed move against the list of dynamic nodes, and move
+ * them out of the way as necessary. Note that this is really a list of
+ * equivalence classes rather than single nodes.
+ */
+
+ unsigned state;
+ /* The current state of this node. One of the @ST@ constants described
+ * below.
+ */
+} mdup_fdinfo;
+
+enum {
+ ST_READY,
+ /* Node has not yet been processed.
+ */
+
+ ST_MARK,
+ /* Node has been reached by the depth-first traversal, but its descriptor
+ * has not yet been moved. This state is used to detect cycles using the
+ * depth-first traversal.
+ */
+
+ ST_DONE,
+ /* Node has been processed completely. We have @want == -1@ or
+ * @want == cur@.
+ */
+
+ ST_BROKEN,
+ /* Node has been clobbered in order to break a cycle. The node's
+ * equivalence class has been remapped to a fresh descriptor which (we
+ * hope) is not equal to any node's @want@. All broken nodes are put on
+ * the dynamic list: if our hope turns out to be misplaced we can remap the
+ * class again.
+ */
+};
+
+/*----- Main code ---------------------------------------------------------*/
+
+/* --- @DO_EQUIVS@ --- *
+ *
+ * Perform @body@ once for each @g@ in the equivalence class of @f@.
+ */
+
+#define DO_EQUIVS(g, f, body) do { \
+ mdup_fdinfo *f_ = (f), *g_ = f_; \
+ do { mdup_fdinfo *g = g_; g_ = g_->eqnext; body; } while (g_ != f_); \
+} while (0)
+
+/* --- @dump@ --- *
+ *
+ * Arguments: @mdup_fdinfo *v@ = pointer to info vector
+ * @size_t n@ = size of vector
+ *
+ * Returns: ---
+ *
+ * Use: Dumps a scary-looking description of the state of @mdup@'s
+ * workings.
+ */
+
+#ifdef DEBUG
+
+#include <stdarg.h>
+#include <stdio.h>
+
+#define D(x) x
+
+static void dump(mdup_fdinfo *v, size_t n, mdup_fdinfo *dhead,
+ const char *fmt, ...)
+{
+ int i;
+ mdup_fdinfo *f, *g;
+ static const char *state[] = { "READY", "MARK", "DONE", "BROKEN" };
+ va_list ap;
+
+#define INDEX(p) ((p) ? (int)((p) - (v)) : -1)
+
+ /* --- Dump the items, fairly raw --- */
+
+ va_start(ap, fmt);
+ fputs("*** ", stdout);
+ vprintf(fmt, ap);
+ putchar('\n');
+ for (i = 0; i < n; i++) {
+ f = &v[i];
+ printf("%3d: %-6s %3d -> %3d; "
+ "equivs: %3d, %3d; up: %3d; down: %3d; dyn: %3d\n",
+ i, state[f->state], f->f->cur, f->f->want,
+ INDEX(f->eqprev), INDEX(f->eqnext),
+ INDEX(f->up), INDEX(f->down), INDEX(f->dlink));
+ }
+ putchar('\n');
+ va_end(ap);
+
+#undef INDEX
+}
+
+#else
+
+#define D(x)
+
+#endif
+
+/* --- @dfs@ --- *
+ *
+ * Arguments: @mdup_fdinfo *f@ = which node to process
+ * @mdup_fdinfo **dhead, ***dtail@ = the dynamic list
+ *
+ * Returns: Zero on success, @-1@ on some OS failure.
+ *
+ * Use: Recursive depth-first traversal of the descriptor graph.
+ *
+ * On exit, the node @f@ will be in state @ST_DONE@ or
+ * @ST_BROKEN@.
+ */
+
+static int dfs(mdup_fdinfo *f, mdup_fdinfo **dhead, mdup_fdinfo ***dtail)
+{
+ mdup_fdinfo *d;
+ mdup_fd *ff;
+ int can_close_p = 1;
+ int fd, ofd;
+ int e;
+
+ /* --- Null pointers need no processing --- *
+ *
+ * Null pointers mark the end of descending chains.
+ */
+
+ if (!f)
+ return (0);
+
+ /* --- Otherwise our behaviour depends on the node's state --- */
+
+ switch (f->state) {
+
+ /* --- The standard processing, in several phases --- */
+
+ case ST_READY:
+
+ /* --- Mark the class as being in-progress --- */
+
+ DO_EQUIVS(g, f, { g->state = ST_MARK; });
+
+ /* --- Ensure that the our proposed destination is clear --- *
+ *
+ * The depth-first traversal will leave the node in @ST_DONE@ or
+ * @ST_BROKEN@ afterwards; either way, its @cur@ will not be same as
+ * our @want@.
+ *
+ * Note that this can move @%\emph{us}@ to @ST_BROKEN@. This is not a
+ * significant problem.
+ */
+
+ DO_EQUIVS(g, f, { if (dfs(g->down, dhead, dtail)) return (-1); });
+
+ /* --- Now the real work can begin --- *
+ *
+ * For each node in the class, copy the descriptor from @cur@ to
+ * @want@. Before doing this, we must move out of the way any (other)
+ * dynamic nodes whose @cur@ matches our @want@.
+ *
+ * Interestingly, this is the only point in the function where we need
+ * nontrivial error handling: if something goes wrong with one of the
+ * @dup2@ calls, we must close the descriptors made so far this pass
+ * before returning.
+ */
+
+ ofd = f->f->cur;
+ DO_EQUIVS(g, f, {
+ ff = g->f;
+ for (d = *dhead; d; d = d->dlink) {
+ if (d != f && d->f->cur == ff->want) {
+ if ((fd = dup(ff->want)) < 0)
+ goto fail;
+ DO_EQUIVS(dd, d, { dd->f->cur = fd; });
+ close(ff->want);
+ }
+ }
+ if (ff->cur == ff->want)
+ can_close_p = 0;
+ else if (dup2(ofd, ff->want) < 0)
+ goto fail;
+ goto ok;
+ fail:
+ e = errno;
+ for (g = g->eqprev; g != f->eqprev; g = g->eqprev) {
+ if (g->f->want != g->f->cur)
+ close(g->f->want);
+ }
+ errno = e;
+ return (-1);
+ ok:;
+ });
+
+ /* --- We're done --- *
+ *
+ * If the original descriptor isn't wanted by anyone we can (and must)
+ * close it. Nodes can now move to @ST_DONE@.
+ */
+
+ if (can_close_p)
+ close(ofd);
+ DO_EQUIVS(g, f, {
+ g->f->cur = g->f->want;
+ g->state = ST_DONE;
+ });
+ break;
+
+ /* --- We have encoutered a cycle --- *
+ *
+ * The caller wants our descriptor. We therefore shunt this entire
+ * equivalence class to a new descriptor, and link it onto the dynamic
+ * list. Mark it as broken so that we don't try to do anything
+ * complicated to it again.
+ */
+
+ case ST_MARK:
+ ofd = f->f->cur;
+ if ((fd = dup(ofd)) < 0)
+ return (-1);
+ DO_EQUIVS(g, f, {
+ g->f->cur = fd;
+ g->state = ST_BROKEN;
+ });
+ f->dlink = **dtail;
+ **dtail = f;
+ close(ofd);
+ break;
+
+ /* --- Nothing to be done here --- *
+ *
+ * @ST_DONE@ nodes have already been completely processed; @ST_BROKEN@
+ * nodes will be fixed up after the main traversal.
+ */
+
+ case ST_DONE:
+ case ST_BROKEN:
+ return (0);
+
+ }
+ return (0);
+}
+
+/* --- @mdup@ --- *
+ *
+ * Arguments: @mdup_fd *v@ = pointer to @mdup_fd@ vector
+ * @size_t n@ = size of vector
+ *
+ * Returns: Zero if successful, @-1@ on failure.
+ *
+ * Use: Rearranges file descriptors.
+ *
+ * The vector @v@ consists of a number of @mdup_fd@ structures.
+ * Each `slot' in the table represents a file. The slot's @cur@
+ * member names the current file descriptor for this file; the
+ * @want@ member is the file descriptor we want to use for it.
+ * if you want to keep a file alive but don't care which
+ * descriptor it ends up with, set @want = -1@. Several slots
+ * may specify the same @cur@ descriptor; but they all have to
+ * declare different @want@s (except that several slots may have
+ * @want = -1@.
+ *
+ * On successful exit, the function will have rearranged the
+ * file descriptors as requested. To reflect this, the @cur@
+ * members will all be set to match the (non-@-1@) @want@
+ * members.
+ *
+ * If there is a failure, then some rearrangement may have been
+ * performed and some not; the @cur@ members are set to reflect
+ * which file descriptors are to be used. The old file
+ * descriptors are closed. (This is different from usual @dup@
+ * behaviour, of course, but essential for reliable error
+ * handling.) If you want to keep a particular source file
+ * descriptor open as well as make a new copy then specify two
+ * slots with the same @cur@, one with @want = cur@ and one with
+ * the desired output descriptor.
+ *
+ * This function works correctly even if the desired remappings
+ * contain cycles.
+ */
+
+int mdup(mdup_fd *v, size_t n)
+{
+ size_t i, j;
+ mdup_fdinfo *vv;
+ mdup_fdinfo *f, *g, *dhead, **dtail;
+ mdup_fd *ff;
+ int rc = -1;
+ int can_close_p;
+ int ofd, fd;
+
+ /* --- Allocate and initialize the table of info nodes --- *
+ *
+ * Each entry @ff@ in the caller's @v@ array will have a corresponding node
+ * @f@ in @vv@ with @f->f = ff@. Initially each node's links are null, and
+ * the node is in the @ST_READY@ state.
+ *
+ * We also initialize a list given by @dhead@ and @dtail@ containing the
+ * entries with `dynamically-assigned' descriptors -- i.e., those whose
+ * values we made up using @dup@. The list lets us detect collisions with
+ * explicitly requested descriptors and move the dynamic ones out of the
+ * way.
+ */
+
+ if ((vv = malloc(sizeof(*vv) * n)) == 0)
+ return (-1);
+
+ dhead = 0;
+ dtail = &dhead;
+ for (i = 0; i < n; i++) {
+ f = &vv[i];
+ f->f = &v[i];
+ f->up = f->down = 0;
+ f->eqnext = f->eqprev = 0;
+ f->state = ST_READY;
+ }
+
+ /* --- Pass one: link the graph together --- *
+ *
+ * Once this pass is complete, the following properties will hold.
+ *
+ * * The nodes which have the same @cur@ are linked together by their
+ * @eqnext@ and @eqprev@ fields into a doubly-linked circular list
+ * representing this equivalence class.
+ *
+ * * @f->up == g@ if and only if @f->f->cur == g->f->want@. (Note that
+ * @want@ fields are unique according to our interface. We detect
+ * violations and exit with @errno == EINVAL@.)
+ *
+ * * If @f->up == g@ then there exists a @ff@ in the same equivalence
+ * class (and therefore on @f@'s @eqnext@ list) as @f@ with
+ * @g->down == ff@.
+ */
+
+ for (i = 0; i < n; i++) {
+ f = &vv[i];
+ if (!f->eqnext)
+ f->eqnext = f->eqprev = f;
+ for (j = 0; j < n; j++) {
+ if (i == j)
+ continue;
+ g = &vv[j];
+ if (f->f->cur == g->f->cur) {
+ if (!g->eqnext) {
+ g->eqnext = f->eqnext;
+ g->eqprev = f;
+ f->eqnext->eqprev = g;
+ f->eqnext = g;
+ }
+ }
+ if (g->f->want == -1)
+ /* fine */;
+ else if (f->f->want == g->f->want) {
+ errno = EINVAL;
+ goto fail;
+ } else if (f->f->cur == g->f->want) {
+ f->up = g;
+ if (!g->down)
+ g->down = f;
+ }
+ }
+ }
+
+ /* --- Pass two: handle don't-care requests --- *
+ *
+ * By the end of this pass, we have the following properties.
+ *
+ * * Every node will be marked @ST_DONE@. This is a temporary abuse of
+ * the @ST_DONE@ state which will be rectified during the next pass.
+ *
+ * * Every node with @want == -1@ will have @cur@ set to a freshly
+ * allocated file descriptor distinct from every previously open file.
+ */
+
+ for (i = 0; i < n; i++) {
+ f = &vv[i];
+ switch (f->state) {
+ case ST_DONE:
+ break;
+ case ST_READY:
+ can_close_p = 1;
+ DO_EQUIVS(g, f, {
+ ff = g->f;
+ ofd = ff->cur;
+ if (ff->want != -1)
+ can_close_p = 0;
+ else {
+ if ((fd = dup(ofd)) < 0)
+ goto fail;
+ ff->cur = fd;
+ }
+ g->state = ST_DONE;
+ });
+ if (can_close_p)
+ close(ofd);
+ break;
+ }
+ }
+
+ /* --- Pass three: restore equivalence classes and @down@ links --- *
+ *
+ * This pass re-establishes the properties from pass one. Because we've
+ * changed some @cur@ members, the equivalence classes will have changed,
+ * so we must fix up the @eqnext@ lists and @down@ links.
+ *
+ * Nodes with @want == -1@ are now finished with (modulo tweaking
+ * dynamically allocated descriptors as we process the others), so we leave
+ * them in @ST_DONE@; other nodes are restored to @ST_READY@.
+ */
+
+ for (i = 0; i < n; i++) {
+ f = &vv[i];
+ ff = f->f;
+ if (ff->want == -1) {
+ f->eqnext->eqprev = f->eqprev;
+ f->eqprev->eqnext = f->eqnext;
+ f->eqnext = f->eqprev = f;
+ f->dlink = *dtail;
+ *dtail = f;
+ } else
+ f->state = ST_READY;
+ }
+
+ /* --- Pass four: main depth-first traversal --- *
+ *
+ * See the description of the function @dfs@ above. After this pass, every
+ * node is in state @ST_DONE@ or @ST_BROKEN@.
+ */
+
+ for (i = 0; i < n; i++) {
+ if (dfs(&vv[i], &dhead, &dtail))
+ goto fail;
+ }
+
+ /* --- Finished --- */
+
+ rc = 0;
+fail:
+ free(vv);
+ return (rc);
+}
+
+/*----- That's all, folks -------------------------------------------------*/
--- /dev/null
+/* -*-c-*-
+ *
+ * Duplicate multiple files
+ *
+ * (c) 2008 Straylight/Edgeware
+ */
+
+/*----- Licensing notice --------------------------------------------------*
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ */
+
+#ifndef MDUP_H
+#define MDUP_H
+
+#ifdef __cplusplus
+ extern "C" {
+#endif
+
+/*----- Data structures ---------------------------------------------------*/
+
+typedef struct mdup_fd {
+ int cur; /* Current file descriptor */
+ int want; /* File descriptor wanted */
+} mdup_fd;
+
+/*----- Functions provided ------------------------------------------------*/
+
+/* --- @mdup@ --- *
+ *
+ * Arguments: @mdup_fd *v@ = pointer to @mdup_fd@ vector
+ * @size_t n@ = size of vector
+ *
+ * Returns: Zero if successful, @-1@ on failure.
+ *
+ * Use: Rearranges file descriptors.
+ *
+ * Use: Rearranges file descriptors.
+ *
+ * The vector @v@ consists of a number of @mdup_fd@ structures.
+ * Each `slot' in the table represents a file. The slot's @cur@
+ * member names the current file descriptor for this file; the
+ * @want@ member is the file descriptor we want to use for it.
+ * if you want to keep a file alive but don't care which
+ * descriptor it ends up with, set @want = -1@. Several slots
+ * may specify the same @cur@ descriptor; but they all have to
+ * declare different @want@s (except that several slots may have
+ * @want = -1@.
+ *
+ * On successful exit, the function will have rearranged the
+ * file descriptors as requested. To reflect this, the @cur@
+ * members will all be set to match the (non-@-1@) @want@
+ * members.
+ *
+ * If there is a failure, then some rearrangement may have been
+ * performed and some not; the @cur@ members are set to reflect
+ * which file descriptors are to be used. The old file
+ * descriptors are closed. (This is different from usual @dup@
+ * behaviour, of course, but essential for reliable error
+ * handling.) If you want to keep a particular source file
+ * descriptor open as well as make a new copy then specify two
+ * slots with the same @cur@, one with @want = cur@ and one with
+ * the desired output descriptor.
+ *
+ * This function works correctly even if the desired remappings
+ * contain cycles.
+ */
+
+extern int mdup(mdup_fd */*v*/, size_t /*n*/);
+
+/*----- That's all, folks -------------------------------------------------*/
+
+#ifdef __cplusplus
+ }
+#endif
+
+#endif
~mdw / mLib / commitdiff