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Many Microsoft employees have contributed to the Windows Subsystem for Linux, this commit is the result of their work since 2016. The entire history of the Windows Subsystem for Linux can't be shared here, but here's an overview of WSL's history after it moved to it own repository in 2021: Number of commits on the main branch: 2930 Number of contributors: 31 Head over https://github.com/microsoft/WSL/releases for a more detailed history of the features added to WSL since 2021.
35 lines
2.6 KiB
Markdown
35 lines
2.6 KiB
Markdown
# Accessing Windows drives from Linux
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WSL offers mountpoints to access Windows drives from Linux. These mountpoints are mounted under `/mnt` by default, and point to the root of Windows drives.
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## Elevated vs non-elevated mountpoints
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Within a distribution, WSL separates between Linux processes that have been created from an elevated (as in administrator level) and from a non-elevated (user level) context.
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This is done by having two separate [mount namespaces](https://man7.org/linux/man-pages/man7/mount_namespaces.7.html) within the distribution. One of them offers an elevated access to Windows drives, and the other offers a non-elevated access to Windows drives.
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When a Linux process is created, [wslservice.exe](wslservice.exe.md) determines its elevation status, and then tell [init](init.md) to create the process in the appropriate mount namespace.
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## Mounting a Windows drive
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*Note: This section only applies to WSL2 distributions. *
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When a [session leader](session-leader.md) is created, [wslsevice.exe](wslservice.exe.md) starts a [plan9](https://9fans.github.io/plan9port/man/man9/intro.html) file server. This file server can be connected to from the WSL2 virtual machine to mount Windows drives.
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When the WSL distribution is created, [wslservice.exe](wslservice.exe.md) uses the `LX_INIT_CONFIGURATION_INFORMATION` message to indicate wether the process that created the distribution is elevated or not. Based on this, [init](init.md) will mount either or the elevated, or un-elevated version of the plan9 server.
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Later when the first command is created in the namespace that hasn't been mounted yet, (either elevated, or non-elevated), [wslservice.exe](wslservice.exe.md) sends a `LxInitMessageRemountDrvfs` to [init](init.md), which tell `init` to mount the other namespace.
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See: `src/windows/service/exe/WslCoreInstance.cpp` and `src/linux/drvfs.cpp`.
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## Mounting a drive from Linux
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As long as the Windows plan9 server is running, drives can be mounted simply by calling [mount](https://linux.die.net/man/8/mount). For instance mounting the C: drive manually can be done via:
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```
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mount -t drvfs C: /tmp/my-mount-point
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```
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Internally, this handled by `/usr/sbin/mount.drvfs`, which is a symlink to `/init`. When `/init` starts, it looks at `argv[0]` to determine which entrypoint to run. If `argv[0]` is `mount.drvfs`, then `/init` runs the `mount.drvfs` entrypoint (see `MountDrvfsEntry()` in `src/linux/init/drvfs.cpp`).
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Depending on the distribution configuration, `mount.drvfs` will either mount the drive as `drvfs` (WSL1), or `plan9`, `virtio-plan9` or `virtiofs` (WSL), depending on [.wslconfig](https://learn.microsoft.com/windows/wsl/wsl-config). |