[libc] implement sys/uio/readv (#124718)

Closes #124694.

This patch adds the `sys/uio/readv` function.
ref:
https://pubs.opengroup.org/onlinepubs/009696699/functions/readv.html

Author: c8ef

libc/config/linux/aarch64/entrypoints.txt

@@ -359,6 +359,7 @@ set(TARGET_LIBC_ENTRYPOINTS
 
     # sys/uio.h entrypoints
     libc.src.sys.uio.writev
+    libc.src.sys.uio.readv
 )
 
 if(LLVM_LIBC_INCLUDE_SCUDO)

libc/config/linux/x86_64/entrypoints.txt

@@ -359,6 +359,7 @@ set(TARGET_LIBC_ENTRYPOINTS
 
     # sys/uio.h entrypoints
     libc.src.sys.uio.writev
+    libc.src.sys.uio.readv
 )
 
 if(LLVM_LIBC_INCLUDE_SCUDO)

libc/include/llvm-libc-macros/limits-macros.h

@@ -239,4 +239,8 @@
 #define _POSIX_ARG_MAX 4096
 #endif
 
+#ifndef IOV_MAX
+#define IOV_MAX 1024
+#endif // IOV_MAX
+
 #endif // LLVM_LIBC_MACROS_LIMITS_MACROS_H

libc/include/sys/uio.yaml

@@ -15,3 +15,11 @@ functions:
       - type: int
       - type: const struct iovec *
       - type: int
+  - name: readv
+    standards:
+      - POSIX
+    return_type: ssize_t
+    arguments:
+      - type: int
+      - type: const struct iovec *
+      - type: int

libc/src/sys/uio/CMakeLists.txt

@@ -8,3 +8,10 @@ add_entrypoint_object(
   DEPENDS
     .${LIBC_TARGET_OS}.writev
 )
+
+add_entrypoint_object(
+  readv
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.readv
+)

libc/src/sys/uio/linux/CMakeLists.txt

@@ -5,10 +5,25 @@ add_entrypoint_object(
   HDRS
     ../writev.h
   DEPENDS
+    libc.hdr.types.ssize_t
+    libc.hdr.types.struct_iovec
     libc.include.sys_syscall
     libc.src.__support.OSUtil.osutil
     libc.src.__support.common
     libc.src.errno.errno
+)
+
+add_entrypoint_object(
+  readv
+  SRCS
+    readv.cpp
+  HDRS
+    ../readv.h
+  DEPENDS
     libc.hdr.types.ssize_t
     libc.hdr.types.struct_iovec
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.__support.common
+    libc.src.errno.errno
 )

libc/src/sys/uio/linux/readv.cpp

@@ -0,0 +1,29 @@
+//===-- Implementation file for readv -------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#include "src/sys/uio/readv.h"
+#include "hdr/types/ssize_t.h"
+#include "hdr/types/struct_iovec.h"
+#include "src/__support/OSUtil/syscall.h"
+#include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
+#include <sys/syscall.h>
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(ssize_t, readv, (int fd, const iovec *iov, int iovcnt)) {
+  long ret = LIBC_NAMESPACE::syscall_impl<long>(SYS_readv, fd, iov, iovcnt);
+  // On failure, return -1 and set errno.
+  if (ret < 0) {
+    libc_errno = static_cast<int>(-ret);
+    return -1;
+  }
+  // On success, return number of bytes read.
+  return static_cast<ssize_t>(ret);
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/sys/uio/linux/writev.cpp

@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 #include "src/sys/uio/writev.h"
+#include "hdr/types/ssize_t.h"
+#include "hdr/types/struct_iovec.h"
 #include "src/__support/OSUtil/syscall.h"
 #include "src/__support/common.h"
 #include "src/errno/libc_errno.h"

libc/src/sys/uio/readv.h

@@ -0,0 +1,22 @@
+//===-- Implementation header for readv -----------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SYS_UIO_READV_H
+#define LLVM_LIBC_SRC_SYS_UIO_READV_H
+
+#include "hdr/types/ssize_t.h"
+#include "hdr/types/struct_iovec.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+ssize_t readv(int fd, const iovec *iov, int iovcnt);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_SYS_UIO_READV_H

libc/test/src/sys/uio/CMakeLists.txt

@@ -1,15 +1,36 @@
 add_custom_target(libc_sys_uio_unittests)
+
 add_libc_unittest(
   writev_test
   SUITE
-  libc_sys_uio_unittests
+    libc_sys_uio_unittests
   SRCS
     writev_test.cpp
   DEPENDS
-    libc.src.errno.errno
+    libc.hdr.types.struct_iovec
     libc.src.__support.common
+    libc.src.errno.errno
+    libc.src.fcntl.open
     libc.src.sys.uio.writev
     libc.src.unistd.close
+    libc.src.unistd.unlink
+    libc.test.UnitTest.ErrnoSetterMatcher
+)
+
+add_libc_unittest(
+  readv_test
+  SUITE
+    libc_sys_uio_unittests
+  SRCS
+    readv_test.cpp
+  DEPENDS
+    libc.hdr.types.struct_iovec
+    libc.src.__support.common
+    libc.src.errno.errno
     libc.src.fcntl.open
+    libc.src.sys.uio.readv
+    libc.src.unistd.close
+    libc.src.unistd.unlink
+    libc.src.unistd.write
     libc.test.UnitTest.ErrnoSetterMatcher
 )