Document DriveInfo.DriveFormat Linux breaking change for .NET 10

docs/core/compatibility/10.0.md

@@ -29,6 +29,7 @@ If you're migrating an app to .NET 10, the breaking changes listed here might af
 | [C# 14 overload resolution with span parameters](core-libraries/10.0/csharp-overload-resolution.md) | Behavioral change | Preview 1 |
 | [Consistent shift behavior in generic math](core-libraries/10.0/generic-math.md) | Behavioral change | Preview 1 |
 | [Default trace context propagator updated to W3C standard](core-libraries/10.0/default-trace-context-propagator.md) | Behavioral change | Preview 4 |
+| [DriveInfo.DriveFormat returns Linux filesystem types](core-libraries/10.0/driveinfo-driveformat-linux.md) | Behavioral change | Preview 6 |
 | [LDAP DirectoryControl parsing is now more stringent](core-libraries/10.0/ldap-directorycontrol-parsing.md) | Behavioral change | Preview 1 |
 | [MacCatalyst version normalization](core-libraries/10.0/maccatalyst-version-normalization.md) | Behavioral change | Preview 1 |
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docs/core/compatibility/core-libraries/10.0/driveinfo-driveformat-linux.md

@@ -0,0 +1,40 @@
+---
+title: "Breaking change: DriveInfo.DriveFormat returns Linux filesystem types"
+description: Learn about the .NET 10 breaking change in core .NET libraries where DriveInfo.DriveFormat on Linux systems returns Linux kernel filesystem type strings instead of mapped magic constants.
+ms.date: 06/24/2025
+---
+# DriveInfo.DriveFormat returns Linux filesystem types
+
+On Linux systems, <xref:System.IO.DriveInfo.DriveFormat?displayProperty=nameWithType> now returns Linux kernel filesystem type strings. These strings represent a more granular representation of the filesystem type than the previous implementation. For example, it's now possible to distinguish between `ext3` and `ext4`.
+
+## Previous behavior
+
+Previously, .NET returned a string representation by mapping magic constants to strings. Because several different filesystem types use the same magic constants, it wasn't possible to distinguish between them.
+
+For cgroup file systems, `DriveFormat` returned `cgroupfs`/`cgroup2fs`. For the SELinux filesystem, the value was `selinux`.
+
+## New behavior
+
+Starting in .NET 10, .NET returns the string representation used by the Linux kernel for the filesystem type.
+
+For cgroup file systems, `DriveFormat` returns `cgroup`/`cgroup2`. For the SELinux filesystem, the value is `selinuxfs`.
+
+## Version introduced
+
+.NET 10 Preview 6
+
+## Type of breaking change
+
+This change is a [behavioral change](../../categories.md#behavioral-change).
+
+## Reason for change
+
+Provide more granular filesystem type information.
+
+## Recommended action
+
+Check and update usages of <xref:System.IO.DriveInfo.DriveFormat?displayProperty=nameWithType> to include the Linux filesystem type strings. On a Linux system, you can read the type strings of the drives from the `/proc/self/mountinfo` file. On each line, the filesystem type string is the first field after the `-` separator.
+
+## Affected APIs
+
+- <xref:System.IO.DriveInfo.DriveFormat?displayProperty=fullName>

docs/core/compatibility/toc.yml

@@ -24,6 +24,8 @@ items:
                 href: core-libraries/10.0/generic-math.md
               - name: Default trace context propagator updated to W3C Standard
                 href: core-libraries/10.0/default-trace-context-propagator.md
+              - name: DriveInfo.DriveFormat returns Linux filesystem types
+                href: core-libraries/10.0/driveinfo-driveformat-linux.md
               - name: LDAP DirectoryControl parsing is now more stringent
                 href: core-libraries/10.0/ldap-directorycontrol-parsing.md
               - name: MacCatalyst version normalization