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https://github.com/tianocore/edk2
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7835e5802a
Replace traditional `#ifndef`/`#define`/`#endif` include guards with
`#pragma` once.
`#pragma once` is a widely supported preprocessor directive that
prevents header files from being included multiple times. It is
supported by all toolchains used to build edk2: GCC, Clang/LLVM, and
MSVC.
Compared to macro-based include guards, `#pragma once`:
- Eliminates the risk of macro name collisions or copy/paste errors
where two headers inadvertently use the same guard macro.
- Eliminate inconsistency in the way include guard macros are named
(e.g., some files use `__FILE_H__`, others use `FILE_H_`, etc.).
- Reduces boilerplate (three lines replaced by one).
- Avoids polluting the macro namespace with guard symbols.
- Can improve build times as the preprocessor can skip re-opening the
file entirely, rather than re-reading it to find the matching
`#endif` ("multiple-include optimization").
- Note that some compilers may already optimize traditional include
guards, by recognzining the idiomatic pattern.
This change is made acknowledging that overall portability of the
code will technically be reduced, as `#pragma once` is not part of the
C/C++ standards.
However, this is considered acceptable given:
1. edk2 already defines a subset of supported compilers in
BaseTools/Conf/tools_def.template, all of which have supported
`#pragma once` for over two decades.
2. There have been concerns raised to the project about inconsistent
include guard naming and potential macro collisions.
Approximate compiler support dates:
- MSVC: Supported since Visual C++ 4.2 (1996)
- GCC: Supported since 3.4 (2004)
(http://gnu.ist.utl.pt/software/gcc/gcc-3.4/changes.html)
- Clang (LLVM based): Since initial release in 2007
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
28 lines
840 B
C
28 lines
840 B
C
/** @file
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Provides a GUID and a data structure that can be used with EFI_FILE_PROTOCOL.GetInfo()
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or EFI_FILE_PROTOCOL.SetInfo() to get or set the system's volume label.
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This GUID is defined in UEFI specification.
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Copyright (c) 2006 - 2018, Intel Corporation. All rights reserved.<BR>
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SPDX-License-Identifier: BSD-2-Clause-Patent
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**/
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#pragma once
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#define EFI_FILE_SYSTEM_VOLUME_LABEL_ID \
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{ \
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0xDB47D7D3, 0xFE81, 0x11d3, {0x9A, 0x35, 0x00, 0x90, 0x27, 0x3F, 0xC1, 0x4D } \
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}
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typedef struct {
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///
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/// The Null-terminated string that is the volume's label.
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///
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CHAR16 VolumeLabel[1];
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} EFI_FILE_SYSTEM_VOLUME_LABEL;
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#define SIZE_OF_EFI_FILE_SYSTEM_VOLUME_LABEL \
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OFFSET_OF (EFI_FILE_SYSTEM_VOLUME_LABEL, VolumeLabel)
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extern EFI_GUID gEfiFileSystemVolumeLabelInfoIdGuid;
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