[vcpkg] implement copy_symlink working for non-elevated processes #12400

Maximus5 · 2020-07-13T12:39:27Z

Function fs::stdfs::copy_symlink used by install_files_and_write_listfile requires the vcpkg process to be running elevated (Windows). Otherwise it always failed with operation not permitted error.

This PR fixes inability to copy symlink in non-elevated processes.
I tried to instal libressl via command

install --recurse libressl[core]:x64-windows

Description of the problem is here: #11949 (comment)

strega-nil · 2020-07-13T18:44:42Z

toolsrc/src/vcpkg/base/files.cpp

+        {
+#if defined(_WIN32)
+            const DWORD flags = SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE;
+            if (!CreateSymbolicLinkW(newpath.c_str(), oldpath.c_str(), flags))


This doesn't work, I don't think -- this has newpath be a symlink for oldpath, which requires that oldpath continues existing; what you really want is newpath to be a symlink to the thing oldpath points to. Maybe you want:

Suggested change

if (!CreateSymbolicLinkW(newpath.c_str(), oldpath.c_str(), flags))

if (!CreateSymbolicLinkW(newpath.c_str(), fs::stdfs::read_symlink(oldpath).c_str(), flags))

Is that okay, that symlink points to packages folder?
In either case fs::stdfs::read_symlink does not work at all: _Map_mode from filesys.cpp does not check FILE_ATTRIBUTE_REPARSE_POINT and does not return file_type::symlink.
Furthermore _Symlink_get returns empty string. It's not implemented yet in my VS 2019.

It's not okay; this is not a copy_symlink at all, it's a create_symlink

Than read_symlink is not a solution, even if it works. Right?

The proper logic will be:

get target of oldpath (it's in packages)

map oldpath to new_oldpath (the original file copied from packages to installed folder)

create symlink newpath targeted to new_oldpath

Right?

It's not okay; this is not a copy_symlink at all, it's a create_symlink

Or what did you mean? What should happen, when vcpkg copies file_v1 + file (symlink pointed to file_v1) from packages to installed folder?

That's not a question I'm interested in answering -- we want copy_symlink to do what copy_symlink says it does. That means, take a file that is a symlink, and copy that file (i.e., create a new file with the same target as the original symlink). copy_symlink needs to do that, not create a new symlink that links to the old file.

std::experimental::filesystem will never be updated to support symlinks; it will be left in a bug for bug compatible with VS2015 state. That implementation had too many bugs and the filesystem TS vs. what got standardized were too divergent to share implementations. std::filesystem is a complete replacement implementation that does support symlinks. As a result _Map_mode will never be changed to enable such support.

The only symlinks that make sense here are relative symlinks, that when copied, still form the correct path in their new location. The "packages" directory is not generally persistent; for example when packages are restored from a binary cache only the 'installed' directory is restored. As a result I don't believe this change will ever persist a symlink correctly :(

strega-nil · 2020-07-14T15:48:50Z

Why can't we use std::filesystem::read_symlink here?

Maximus5 · 2020-07-14T16:44:04Z

Why can't we use std::filesystem::read_symlink here?

std::filesystem::read_symlink is available from C++17 only.
The project properties don't allow this language standard.

and std::filesystem::experimental::read_symlink just doesn't work - it returns empty string.

toolsrc/src/vcpkg/base/files.cpp

Co-authored-by: nicole mazzuca <mazzucan@outlook.com>

strega-nil

Just some more minor changes, then I'm good with merging :)

It's still not perfect; given a -> b -> c (a, b symlinks with a pointing to b, b pointing to c), copy_symlink(a, d) will give you d -> c, whereas in a perfect world you'd get d -> b -> c. Unfortunately, Windows does not support this feature without using DeviceIoControl, and so I'm willing to deal with this for now. When we rewrite the files code to remove std::filesystem, that'll be a thing to do -- specifically, using https://docs.microsoft.com/en-us/windows-hardware/drivers/ifs/fsctl-get-reparse-point

toolsrc/src/vcpkg/base/files.cpp

Co-authored-by: nicole mazzuca <mazzucan@outlook.com>

ras0219-msft · 2020-07-15T22:13:57Z

Thanks everyone!

BillyONeal · 2020-07-28T19:31:22Z

Unfortunately this implements read_symlink as canonical which breaks relative symlinks -- so it now succeeds but all the symlinks point into the packages tree which is about to be deleted.

Maximus5 · 2020-07-28T20:14:18Z

I've asked about symlinks pointed to packages folder.
#12400 (comment)

BillyONeal · 2020-07-28T20:31:34Z

@Maximus5 I see; sorry for not noticing before; I just found this PR through a 'git blame'.

…crosoft#12400) * [vcpkg] implement copy_symlink working for non-elevated processes * [vcpkg] read_symlink Windows implementation * [vcpkg] normalize_path on Windows only * Update toolsrc/src/vcpkg/base/files.cpp Co-authored-by: nicole mazzuca <mazzucan@outlook.com> * Update toolsrc/src/vcpkg/base/files.cpp Co-authored-by: nicole mazzuca <mazzucan@outlook.com> * Update toolsrc/src/vcpkg/base/files.cpp Co-authored-by: nicole mazzuca <mazzucan@outlook.com> * remove normalization * Update toolsrc/src/vcpkg/base/files.cpp Co-authored-by: nicole mazzuca <mazzucan@outlook.com> * Update toolsrc/src/vcpkg/base/files.cpp Co-authored-by: nicole mazzuca <mazzucan@outlook.com> * Update toolsrc/src/vcpkg/base/files.cpp Co-authored-by: nicole mazzuca <mazzucan@outlook.com> * Update toolsrc/src/vcpkg/base/files.cpp Co-authored-by: nicole mazzuca <mazzucan@outlook.com> * Update toolsrc/src/vcpkg/base/files.cpp Co-authored-by: nicole mazzuca <mazzucan@outlook.com> * use unique_ptr * comments Co-authored-by: nicole mazzuca <mazzucan@outlook.com>

[vcpkg] implement copy_symlink working for non-elevated processes

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ras0219-msft requested a review from strega-nil July 13, 2020 17:53

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LilyWangL assigned NancyLi1013 Jul 14, 2020

Maximus5 added 2 commits July 14, 2020 10:06

[vcpkg] read_symlink Windows implementation

108ae60

[vcpkg] normalize_path on Windows only

f7bbc5f

Maximus5 requested a review from strega-nil July 14, 2020 08:14

strega-nil suggested changes Jul 14, 2020

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Maximus5 and others added 4 commits July 14, 2020 19:20

Update toolsrc/src/vcpkg/base/files.cpp

a579898

Co-authored-by: nicole mazzuca <mazzucan@outlook.com>

Update toolsrc/src/vcpkg/base/files.cpp

e2f05a2

Co-authored-by: nicole mazzuca <mazzucan@outlook.com>

Update toolsrc/src/vcpkg/base/files.cpp

b548fb4

Co-authored-by: nicole mazzuca <mazzucan@outlook.com>

remove normalization

04a0978

strega-nil suggested changes Jul 14, 2020

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Maximus5 and others added 7 commits July 14, 2020 19:55

Update toolsrc/src/vcpkg/base/files.cpp

4a20d10

Co-authored-by: nicole mazzuca <mazzucan@outlook.com>

Update toolsrc/src/vcpkg/base/files.cpp

9420093

Co-authored-by: nicole mazzuca <mazzucan@outlook.com>

Update toolsrc/src/vcpkg/base/files.cpp

1c13352

Co-authored-by: nicole mazzuca <mazzucan@outlook.com>

Update toolsrc/src/vcpkg/base/files.cpp

738778e

Co-authored-by: nicole mazzuca <mazzucan@outlook.com>

Update toolsrc/src/vcpkg/base/files.cpp

7dfb7ca

Co-authored-by: nicole mazzuca <mazzucan@outlook.com>

use unique_ptr

db575c6

comments

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Maximus5 requested a review from strega-nil July 15, 2020 07:41

strega-nil approved these changes Jul 15, 2020

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strega-nil added category:vcpkg-bug The issue is with the vcpkg system (including helper scripts in `scripts/cmake/`) info:reviewed Pull Request changes follow basic guidelines labels Jul 15, 2020

ras0219-msft merged commit 8254d3b into microsoft:master Jul 15, 2020

strega-nil mentioned this pull request Jul 27, 2020

[vcpkg] Fix build on Windows 8.1 SDK #12586

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[vcpkg] implement copy_symlink working for non-elevated processes #12400

[vcpkg] implement copy_symlink working for non-elevated processes #12400

Maximus5 commented Jul 13, 2020

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ras0219-msft commented Jul 15, 2020

BillyONeal commented Jul 28, 2020

Maximus5 commented Jul 28, 2020

BillyONeal commented Jul 28, 2020

	if (!CreateSymbolicLinkW(newpath.c_str(), oldpath.c_str(), flags))
	if (!CreateSymbolicLinkW(newpath.c_str(), fs::stdfs::read_symlink(oldpath).c_str(), flags))

[vcpkg] implement copy_symlink working for non-elevated processes #12400

[vcpkg] implement copy_symlink working for non-elevated processes #12400

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