Add truncateat(2).

Linux doesn't have this, but since I do truncate(2) in the kernel, it would
be more consistent to do it 'at'-style. (I will remove truncate(2) from the
kernel and let libc call truncateat(2) soon anyway).

libc/Makefile

@@ -197,6 +197,7 @@ stat.o \
 stdio.o \
 tfork.o \
 time.o \
+truncateat.o \
 truncate.o \
 umask.o \
 unlinkat.o \

libc/include/unistd.h

@@ -176,6 +176,7 @@ ssize_t read(int, void*, size_t);
 int rmdir(const char*);
 unsigned sleep(unsigned);
 int truncate(const char*, off_t);
+int truncateat(int dirfd, const char*, off_t);
 #if __POSIX_OBSOLETE <= 200112 || defined(_SORTIX_SOURCE)
 int usleep(useconds_t useconds);
 #endif

libc/truncateat.cpp

@@ -0,0 +1,34 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2012.
+
+    This file is part of the Sortix C Library.
+
+    The Sortix C Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or (at your
+    option) any later version.
+
+    The Sortix C Library 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 Lesser General Public
+    License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
+
+    truncateat.cpp
+    Truncates a file to a specific size.
+
+*******************************************************************************/
+
+#include <sys/types.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+DEFN_SYSCALL3(int, sys_truncateat, SYSCALL_TRUNCATEAT, int, const char*, off_t);
+
+extern "C" int truncateat(int dirfd, const char* pathname, off_t length)
+{
+	return sys_truncateat(dirfd, pathname, length);
+}

sortix/include/sortix/syscallnum.h

@@ -86,6 +86,7 @@
 #define SYSCALL_FACCESSAT 62
 #define SYSCALL_MKDIRAT 63
 #define SYSCALL_FCHDIR 64
-#define SYSCALL_MAX_NUM 65 /* index of highest constant + 1 */
+#define SYSCALL_TRUNCATEAT 65
+#define SYSCALL_MAX_NUM 66 /* index of highest constant + 1 */
 
 #endif

sortix/io.cpp

@@ -226,14 +226,15 @@ static int sys_rmdir(const char* path)
 	return sys_unlinkat(AT_FDCWD, path, AT_REMOVEDIR);
 }
 
-static int sys_truncate(const char* path, off_t length)
+static int sys_truncateat(int dirfd, const char* path, off_t length)
 {
 	char* pathcopy = GetStringFromUser(path);
 	if ( !pathcopy )
 		return -1;
 	ioctx_t ctx; SetupUserIOCtx(&ctx);
 	const char* relpath = pathcopy;
-	Ref<Descriptor> from = PrepareLookup(&relpath);
+	Ref<Descriptor> from = PrepareLookup(&relpath, dirfd);
+	if ( !from ) { delete[] pathcopy; return -1; }
 	Ref<Descriptor> desc = from->open(&ctx, relpath, O_WRONLY);
 	delete[] pathcopy;
 	if ( !desc )
@@ -241,6 +242,11 @@ static int sys_truncate(const char* path, off_t length)
 	return desc->truncate(&ctx, length);
 }
 
+static int sys_truncate(const char* path, off_t length)
+{
+	return sys_truncateat(AT_FDCWD, path, length);
+}
+
 static int sys_ftruncate(int fd, off_t length)
 {
 	Ref<Descriptor> desc = CurrentProcess()->GetDescriptor(fd);
@@ -475,6 +481,7 @@ void Init()
 	Syscall::Register(SYSCALL_SETTERMMODE, (void*) sys_settermmode);
 	Syscall::Register(SYSCALL_STAT, (void*) sys_stat);
 	Syscall::Register(SYSCALL_TCGETWINSIZE, (void*) sys_tcgetwinsize);
+	Syscall::Register(SYSCALL_TRUNCATEAT, (void*) sys_truncateat);
 	Syscall::Register(SYSCALL_TRUNCATE, (void*) sys_truncate);
 	Syscall::Register(SYSCALL_UNLINKAT, (void*) sys_unlinkat);
 	Syscall::Register(SYSCALL_UNLINK, (void*) sys_unlink);