Fix symlink resolution when mounting

[Sploder12]

fixes #1722

Symbolic links are now resolved when performing a mount.
Previously they were not resolved.

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.92%. Comparing base (2f84668) to head (ccac3af).

Files with missing lines	Patch %	Lines
src/utils/vm_mount.cpp	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3673      +/-   ##
==========================================
- Coverage   88.92%   88.92%   -0.01%     
==========================================
  Files         254      254              
  Lines       14299    14309      +10     
==========================================
+ Hits        12716    12724       +8     
- Misses       1583     1585       +2     

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[ricab]

Thank you Trevor! Superficial review from my side, but it looks like it's headed in the right direction. I have a couple of comments inline.

[ricab]

This one doesn't help much unless you change make_native_mount_handler to take by value and move too. Otherwise you're asking for one extra temporary.

[ricab]

Hey Trevor, this works well for what it does and the code looks good. However, currently it covers only paths ending in a symlink. I guess we should cover symlinks anywhere in the path, don't you think?

ricab@ricab-XPS-9320:~/tmp/asdf $ ln -s .. l4
ricab@ricab-XPS-9320:~/tmp/asdf $ cd
ricab@ricab-XPS-9320:~ $ mp mount tmp/asdf/l4/subl-mdpreview/ amazed-topi:l4
ricab@ricab-XPS-9320:~ $ mp info amazed-topi
Name:           amazed-topi
State:          Running
Snapshots:      2
IPv4:           10.251.95.73
Release:        Ubuntu 24.04.1 LTS
Image hash:     78547d336e4c (Ubuntu 24.04 LTS)
CPU(s):         2
Load:           0.00 0.00 0.00
Disk usage:     2.0GiB out of 4.8GiB
Memory usage:   342.3MiB out of 955.7MiB
Mounts:         /home/ricab/tmp/asdf/l4/subl-mdpreview => l4
                    UID map: 1000:default
                    GID map: 1000:default

I expected the source to become just /home/ricab/tmp/subl-mdpreview

[ricab]

This would end up being shown to the user, right? If so, I would try to make it more user friendly. Perhaps:

Suggested change

	fmt::format("Mount symlink source path \"{}\" could not be made weakly canonical: {}.",
	fmt::format("Could not resolve symlinks in mount source path \"{}\": {}.",

[ricab]

Hey Trevor, a quick experiment I did:

#include <filesystem>
#include <iostream>

using namespace std;
namespace fs = std::filesystem;

int main()
{
  // l4 -> ..
  // l2 -> ../subl-mdpreview
  auto src_path = "/home/ricab/tmp/asdf/l4/asdf/l4/asdf/l2/";

  error_code ec{};
  auto dst_path = fs::weakly_canonical(src_path, ec);

  if (!ec)
    cout << "\"" << src_path << "\" == " << dst_path << endl;

  // prints "/home/ricab/tmp/asdf/l4/asdf/l4/asdf/l2/" == "/home/ricab/tmp/subl-mdpreview"

  return bool(ec);
}

[Sploder12]

I wonder if we should check elsewhere in the repo for usage of \"{}\" since a string like Hello\\ could cause issues (becomes "Hello\"). WDYT?