Add preadv2/pwritev2 wrappers.

They're in glibc, though not in musl.

Also add basic doc comments to the whole of <sys/uio.h>.

Bug: http://b/203002492
Test: treehugger
Change-Id: Ic607f7f349e5b7c9bf66c25b7bd68f827da530d6

libc/Android.bp

@@ -1121,6 +1121,7 @@ cc_library_static {
         "bionic/posix_fallocate.cpp",
         "bionic/posix_madvise.cpp",
         "bionic/posix_timers.cpp",
+        "bionic/preadv_pwritev.cpp",
         "bionic/ptrace.cpp",
         "bionic/pty.cpp",
         "bionic/raise.cpp",

libc/SYSCALLS.TXT

@@ -97,13 +97,14 @@ ssize_t     pwrite64(int, void*, size_t, off64_t) lp32
 ssize_t     pwrite64|pwrite(int, void*, size_t, off_t) lp64
 
 # On LP32, preadv/pwritev don't use off64_t --- they use pairs of 32-bit
-# arguments to avoid problems on architectures like ARM where 64-bit arguments
+# arguments to avoid problems on architectures like arm32 where 64-bit arguments
 # must be in a register pair starting with an even-numbered register.
 # See linux/fs/read_write.c and https://lwn.net/Articles/311630/.
-ssize_t     __preadv64:preadv(int, const struct iovec*, int, long, long) lp32
+# Note that there's an unused always-0 second long even on LP64!
-ssize_t     preadv|preadv64(int, const struct iovec*, int, off_t) lp64
+ssize_t     __preadv64:preadv(int, const struct iovec*, int, long, long) all
-ssize_t     __pwritev64:pwritev(int, const struct iovec*, int, long, long) lp32
+ssize_t     __pwritev64:pwritev(int, const struct iovec*, int, long, long) all
-ssize_t     pwritev|pwritev64(int, const struct iovec*, int, off_t) lp64
+ssize_t     __preadv64v2:preadv2(int, const struct iovec*, int, long, long, int) all
+ssize_t     __pwritev64v2:pwritev2(int, const struct iovec*, int, long, long, int) all
 
 int         __close:close(int)  all
 pid_t       __getpid:getpid()  all

libc/bionic/legacy_32_bit_support.cpp

@@ -45,8 +45,6 @@
 
 // System calls we need.
 extern "C" int __llseek(int, unsigned long, unsigned long, off64_t*, int);
-extern "C" int __preadv64(int, const struct iovec*, int, long, long);
-extern "C" int __pwritev64(int, const struct iovec*, int, long, long);
 
 // For lseek64 we need to use the llseek system call which splits the off64_t in two and
 // returns the off64_t result via a pointer because 32-bit kernels can't return 64-bit results.
@@ -70,23 +68,6 @@ ssize_t pwrite(int fd, const void* buf, size_t byte_count, off_t offset) {
   return pwrite64(fd, buf, byte_count, static_cast<off64_t>(offset));
 }
 
-// On LP32, there is no off_t preadv/pwritev, and even the 64-bit preadv/pwritev
-// don't use off64_t (see SYSCALLS.TXT for more). Here, this means that we need
-// to implement all four functions because the two system calls don't match any
-// of the userspace functions. Unlike llseek, the pair is split lo-hi, not hi-lo.
-ssize_t preadv(int fd, const struct iovec* ios, int count, off_t offset) {
-  return preadv64(fd, ios, count, offset);
-}
-ssize_t preadv64(int fd, const struct iovec* ios, int count, off64_t offset) {
-  return __preadv64(fd, ios, count, offset, offset >> 32);
-}
-ssize_t pwritev(int fd, const struct iovec* ios, int count, off_t offset) {
-  return pwritev64(fd, ios, count, offset);
-}
-ssize_t pwritev64(int fd, const struct iovec* ios, int count, off64_t offset) {
-  return __pwritev64(fd, ios, count, offset, offset >> 32);
-}
-
 // There is no fallocate for 32-bit off_t, so we need to widen and call fallocate64.
 int fallocate(int fd, int mode, off_t offset, off_t length) {
   return fallocate64(fd, mode, static_cast<off64_t>(offset), static_cast<off64_t>(length));

libc/bionic/preadv_pwritev.cpp

@@ -0,0 +1,91 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/uio.h>
+
+// System calls we need.
+extern "C" int __preadv64(int, const struct iovec*, int, long, long);
+extern "C" int __preadv64v2(int, const struct iovec*, int, long, long, int);
+extern "C" int __pwritev64(int, const struct iovec*, int, long, long);
+extern "C" int __pwritev64v2(int, const struct iovec*, int, long, long, int);
+
+// There is no 32-bit off_t preadv/pwritev (even on LP32).
+// To avoid 32-bit ABI issues about which register pairs you're allowed
+// to pass 64-bit values in, the kernel just takes two `long` arguments --
+// which are int32_t for LP32, remember -- and stitches them together.
+// It even does this for LP64, taking a second unused always-zero `long`.
+// (The first long was int64_t, which is the same as off64_t.)
+// The pair is split lo-hi (not hi-lo, as llseek is).
+
+ssize_t preadv(int fd, const struct iovec* ios, int count, off_t offset) {
+  return preadv64(fd, ios, count, offset);
+}
+
+ssize_t preadv64(int fd, const struct iovec* ios, int count, off64_t offset) {
+#if defined(__LP64__)
+  return __preadv64(fd, ios, count, offset, 0);
+#else
+  return __preadv64(fd, ios, count, offset, offset >> 32);
+#endif
+}
+
+ssize_t pwritev(int fd, const struct iovec* ios, int count, off_t offset) {
+  return pwritev64(fd, ios, count, offset);
+}
+
+ssize_t pwritev64(int fd, const struct iovec* ios, int count, off64_t offset) {
+#if defined(__LP64__)
+  return __pwritev64(fd, ios, count, offset, 0);
+#else
+  return __pwritev64(fd, ios, count, offset, offset >> 32);
+#endif
+}
+
+ssize_t preadv2(int fd, const struct iovec* ios, int count, off_t offset, int flags) {
+  return preadv64v2(fd, ios, count, offset, flags);
+}
+
+ssize_t preadv64v2(int fd, const struct iovec* ios, int count, off64_t offset, int flags) {
+#if defined(__LP64__)
+  return __preadv64v2(fd, ios, count, offset, 0, flags);
+#else
+  return __preadv64v2(fd, ios, count, offset, offset >> 32, flags);
+#endif
+}
+
+ssize_t pwritev2(int fd, const struct iovec* ios, int count, off_t offset, int flags) {
+  return pwritev64v2(fd, ios, count, offset, flags);
+}
+
+ssize_t pwritev64v2(int fd, const struct iovec* ios, int count, off64_t offset, int flags) {
+#if defined(__LP64__)
+  return __pwritev64v2(fd, ios, count, offset, 0, flags);
+#else
+  return __pwritev64v2(fd, ios, count, offset, offset >> 32, flags);
+#endif
+}

libc/include/sys/uio.h

@@ -26,8 +26,12 @@
  * SUCH DAMAGE.
  */
 
-#ifndef _SYS_UIO_H_
+#pragma once
-#define _SYS_UIO_H_
+
+/**
+ * @file sys/uio.h
+ * @brief Multi-buffer ("vector") I/O operations using `struct iovec`.
+ */
 
 #include <sys/cdefs.h>
 #include <sys/types.h>
@@ -35,21 +39,124 @@
 
 __BEGIN_DECLS
 
+/**
+ * [readv(2)](http://man7.org/linux/man-pages/man2/readv.2.html) reads
+ * from an fd into the `__count` buffers described by `__iov`.
+ *
+ * Returns the number of bytes read on success,
+ * and returns -1 and sets `errno` on failure.
+ */
 ssize_t readv(int __fd, const struct iovec* __iov, int __count);
+
+/**
+ * [writev(2)](http://man7.org/linux/man-pages/man2/writev.2.html) writes
+ * to an fd from the `__count` buffers described by `__iov`.
+ *
+ * Returns the number of bytes written on success,
+ * and returns -1 and sets `errno` on failure.
+ */
 ssize_t writev(int __fd, const struct iovec* __iov, int __count);
 
 #if defined(__USE_GNU)
-ssize_t preadv(int __fd, const struct iovec* __iov, int __count, off_t __offset) __RENAME_IF_FILE_OFFSET64(preadv64) __INTRODUCED_IN(24);
-ssize_t pwritev(int __fd, const struct iovec* __iov, int __count, off_t __offset) __RENAME_IF_FILE_OFFSET64(pwritev64) __INTRODUCED_IN(24);
-ssize_t preadv64(int __fd, const struct iovec* __iov, int __count, off64_t __offset) __INTRODUCED_IN(24);
-ssize_t pwritev64(int __fd, const struct iovec* __iov, int __count, off64_t __offset) __INTRODUCED_IN(24);
-#endif
 
-#if defined(__USE_GNU)
+/**
+ * [preadv(2)](http://man7.org/linux/man-pages/man2/preadv.2.html) reads
+ * from an fd into the `__count` buffers described by `__iov`, starting at
+ * offset `__offset` into the file.
+ *
+ * Returns the number of bytes read on success,
+ * and returns -1 and sets `errno` on failure.
+ *
+ * Available since API level 24.
+ */
+ssize_t preadv(int __fd, const struct iovec* __iov, int __count, off_t __offset) __RENAME_IF_FILE_OFFSET64(preadv64) __INTRODUCED_IN(24);
+
+/**
+ * [pwritev(2)](http://man7.org/linux/man-pages/man2/pwritev.2.html) writes
+ * to an fd from the `__count` buffers described by `__iov`, starting at offset
+ * `__offset` into the file.
+ *
+ * Returns the number of bytes written on success,
+ * and returns -1 and sets `errno` on failure.
+ *
+ * Available since API level 24.
+ */
+ssize_t pwritev(int __fd, const struct iovec* __iov, int __count, off_t __offset) __RENAME_IF_FILE_OFFSET64(pwritev64) __INTRODUCED_IN(24);
+
+/**
+ * Like preadv() but with a 64-bit offset even in a 32-bit process.
+ *
+ * Available since API level 24.
+ */
+ssize_t preadv64(int __fd, const struct iovec* __iov, int __count, off64_t __offset) __INTRODUCED_IN(24);
+
+/**
+ * Like pwritev() but with a 64-bit offset even in a 32-bit process.
+ *
+ * Available since API level 24.
+ */
+ssize_t pwritev64(int __fd, const struct iovec* __iov, int __count, off64_t __offset) __INTRODUCED_IN(24);
+
+/**
+ * [preadv2(2)](http://man7.org/linux/man-pages/man2/preadv2.2.html) reads
+ * from an fd into the `__count` buffers described by `__iov`, starting at
+ * offset `__offset` into the file, with the given flags.
+ *
+ * Returns the number of bytes read on success,
+ * and returns -1 and sets `errno` on failure.
+ *
+ * Available since API level 33.
+ */
+ssize_t preadv2(int __fd, const struct iovec* __iov, int __count, off_t __offset, int __flags) __RENAME_IF_FILE_OFFSET64(preadv64v2) __INTRODUCED_IN(33);
+
+/**
+ * [pwritev2(2)](http://man7.org/linux/man-pages/man2/pwritev2.2.html) writes
+ * to an fd from the `__count` buffers described by `__iov`, starting at offset
+ * `__offset` into the file, with the given flags.
+ *
+ * Returns the number of bytes written on success,
+ * and returns -1 and sets `errno` on failure.
+ *
+ * Available since API level 33.
+ */
+ssize_t pwritev2(int __fd, const struct iovec* __iov, int __count, off_t __offset, int __flags) __RENAME_IF_FILE_OFFSET64(pwritev64v2) __INTRODUCED_IN(33);
+
+/**
+ * Like preadv2() but with a 64-bit offset even in a 32-bit process.
+ *
+ * Available since API level 33.
+ */
+ssize_t preadv64v2(int __fd, const struct iovec* __iov, int __count, off64_t __offset, int __flags) __INTRODUCED_IN(33);
+
+/**
+ * Like pwritev2() but with a 64-bit offset even in a 32-bit process.
+ *
+ * Available since API level 33.
+ */
+ssize_t pwritev64v2(int __fd, const struct iovec* __iov, int __count, off64_t __offset, int __flags) __INTRODUCED_IN(33);
+
+/**
+ * [process_vm_readv(2)](http://man7.org/linux/man-pages/man2/process_vm_readv.2.html)
+ * reads from the address space of another process.
+ *
+ * Returns the number of bytes read on success,
+ * and returns -1 and sets `errno` on failure.
+ *
+ * Available since API level 23.
+ */
 ssize_t process_vm_readv(pid_t __pid, const struct iovec* __local_iov, unsigned long __local_iov_count, const struct iovec* __remote_iov, unsigned long __remote_iov_count, unsigned long __flags) __INTRODUCED_IN(23);
+
+/**
+ * [process_vm_writev(2)](http://man7.org/linux/man-pages/man2/process_vm_writev.2.html)
+ * writes to the address space of another process.
+ *
+ * Returns the number of bytes read on success,
+ * and returns -1 and sets `errno` on failure.
+ *
+ * Available since API level 23.
+ */
 ssize_t process_vm_writev(pid_t __pid, const struct iovec* __local_iov, unsigned long __local_iov_count, const struct iovec* __remote_iov, unsigned long __remote_iov_count, unsigned long __flags) __INTRODUCED_IN(23);
+
 #endif
 
 __END_DECLS
-
-#endif

libc/libc.map.txt

@@ -1565,6 +1565,14 @@ LIBC_S { # introduced=S
     process_madvise;
 } LIBC_R;
 
+LIBC_T { # introduced=Tiramisu
+  global:
+    preadv2;
+    preadv64v2;
+    pwritev2;
+    pwritev64v2;
+} LIBC_S;
+
 LIBC_PRIVATE {
   global:
     __accept4; # arm x86

tests/sys_uio_test.cpp

@@ -16,7 +16,11 @@
 
 #include <gtest/gtest.h>
 
+#include <errno.h>
+#include <string.h>
+#include <sys/types.h>
 #include <sys/uio.h>
+#include <unistd.h>
 
 #include <android-base/file.h>
 
@@ -68,6 +72,42 @@ TEST(sys_uio, preadv64_pwritev64) {
   TestPreadVPwriteV(preadv64, pwritev64);
 }
 
+template <typename ReadFn, typename WriteFn>
+void TestPreadV2PwriteV2(ReadFn read_fn, WriteFn write_fn) {
+  TemporaryFile tf;
+
+  char buf[] = "world";
+  iovec ios[] = {{buf, 5}};
+
+  ASSERT_EQ(5, write_fn(tf.fd, ios, 1, 5, 0)) << strerror(errno);
+  ASSERT_EQ(0, lseek(tf.fd, 0, SEEK_CUR));
+
+  strcpy(buf, "hello");
+  ASSERT_EQ(5, write_fn(tf.fd, ios, 1, 0, 0)) << strerror(errno);
+  ASSERT_EQ(0, lseek(tf.fd, 0, SEEK_CUR));
+
+  ASSERT_EQ(5, read_fn(tf.fd, ios, 1, 5, 0)) << strerror(errno);
+  ASSERT_STREQ("world", buf);
+  ASSERT_EQ(5, read_fn(tf.fd, ios, 1, 0, 0)) << strerror(errno);
+  ASSERT_STREQ("hello", buf);
+}
+
+TEST(sys_uio, preadv2_pwritev2) {
+#if defined(__BIONIC__)
+  TestPreadV2PwriteV2(preadv2, pwritev2);
+#else
+  GTEST_SKIP() << "preadv2/pwritev2 not available";
+#endif
+}
+
+TEST(sys_uio, preadv64v2_pwritev64v2) {
+#if defined(__BIONIC__)
+  TestPreadV2PwriteV2(preadv64v2, pwritev64v2);
+#else
+  GTEST_SKIP() << "preadv2/pwritev2 not available";
+#endif
+}
+
 TEST(sys_uio, process_vm_readv) {
   ASSERT_EQ(0, process_vm_readv(0, nullptr, 0, nullptr, 0, 0));