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[Xen-devel] [PATCH v3 3/9] docs: add feature document for Xen hypervisor sysfs-like support



On the 2019 Xen developer summit there was agreement that the Xen
hypervisor should gain support for a hierarchical name-value store
similar to the Linux kernel's sysfs.

In the beginning there should only be basic support: entries can be
added from the hypervisor itself only, there is a simple hypercall
interface to read the data.

Add a feature document for setting the base of a discussion regarding
the desired functionality and the entries to add.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V1:
- remove the "--" prefixes of the sub-commands of the user tool
  (Jan Beulich)
- rename xenfs to xenhypfs (Jan Beulich)
- add "tree" and "write" options to user tool

V2:
- move example tree to the paths description (Ian Jackson)
- specify allowed characters for keys and values (Ian Jackson)

V3:
- correct introduction (writable entries)
---
 docs/features/hypervisorfs.pandoc | 86 +++++++++++++++++++++++++++++++++++
 docs/misc/hypfs-paths.pandoc      | 95 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 181 insertions(+)
 create mode 100644 docs/features/hypervisorfs.pandoc
 create mode 100644 docs/misc/hypfs-paths.pandoc

diff --git a/docs/features/hypervisorfs.pandoc 
b/docs/features/hypervisorfs.pandoc
new file mode 100644
index 0000000000..8e5deaacfb
--- /dev/null
+++ b/docs/features/hypervisorfs.pandoc
@@ -0,0 +1,86 @@
+% Hypervisor FS
+% Revision 1
+
+\clearpage
+
+# Basics
+---------------- ---------------------
+         Status: **Supported**
+
+  Architectures: all
+
+     Components: Hypervisor, toolstack
+---------------- ---------------------
+
+# Overview
+
+The Hypervisor FS is a hierarchical name-value store for reporting
+information to guests, especially dom0.  It is similar to the Linux
+kernel's sysfs. Entries and directories are created by the hypervisor,
+while the toolstack is able to use a hypercall to query the entry
+values or (if allowed by the hypervisor) to modify them.
+
+# User details
+
+With:
+
+    xenhypfs ls <path>
+
+the user can list the entries of a specific path of the FS. Using:
+
+    xenhypfs cat <path>
+
+the content of an entry can be retrieved. Using:
+
+    xenhypfs write <path> <string>
+
+a writable entry can be modified. With:
+
+    xenhypfs tree
+
+the complete Hypervisor FS entry tree can be printed.
+
+The FS paths are documented in `docs/misc/hypfs-paths.pandoc`.
+
+# Technical details
+
+Access to the hypervisor filesystem is done via the stable new hypercall
+__HYPERVISOR_filesystem_op.
+
+* hypercall interface specification
+    * `xen/include/public/filesystem.h`
+* hypervisor internal files
+    * `xen/include/xen/filesystem.h`
+    * `xen/common/filesystem.c`
+* `libxenhypfs`
+    * `tools/libs/libxenhypfs/*`
+* `xenhypfs`
+    * `tools/misc/xenhypfs.c`
+* path documentation
+    * `docs/misc/hypfs-paths.pandoc`
+ 
+# Testing
+
+Any new parameters or hardware mitigations should be verified to show up
+correctly in the filesystem.
+
+# Areas for improvement
+
+* More detailed access rights
+* Entries per domain and/or per cpupool
+
+# Known issues
+
+* None
+
+# References
+
+* None
+
+# History
+
+------------------------------------------------------------------------
+Date       Revision Version  Notes
+---------- -------- -------- -------------------------------------------
+2019-10-02 1        Xen 4.13 Document written
+---------- -------- -------- -------------------------------------------
diff --git a/docs/misc/hypfs-paths.pandoc b/docs/misc/hypfs-paths.pandoc
new file mode 100644
index 0000000000..67de8d2cf8
--- /dev/null
+++ b/docs/misc/hypfs-paths.pandoc
@@ -0,0 +1,95 @@
+# Xenhypfs Paths
+
+This document attempts to define all the paths which are available
+in the Xen hypervisor file system (hypfs).
+
+The hypervisor file system can be accessed via the xenhypfs tool.
+
+## Notation
+
+The hypervisor file system is similar to the Linux kernel's sysfs.
+In this document directories are always specified with a trailing "/".
+
+The following notation conventions apply:
+
+        DIRECTORY/
+
+        PATH = VALUES [TAGS]
+
+The first syntax defines a directory. It normally contains related
+entries and the general scope of the directory is described.
+
+The second syntax defines a file entry containing values which are
+either set by the hypervisor or, if the file is writable, can be set
+by the user.
+
+PATH can contain simple regex constructs following the Perl compatible
+regexp syntax described in pcre(3) or perlre(1).
+
+A hypervisor file system entry name can be any 0-delimited byte string
+not containing any '/' character. The names "." and ".." are reserved
+for file system internal use.
+
+VALUES are strings and can take the following forms:
+
+* STRING -- an arbitrary 0-delimited byte string.
+* INTEGER -- An integer, in decimal representation unless otherwise
+  noted.
+* "a literal string" -- literal strings are contained within quotes.
+* (VALUE | VALUE | ... ) -- a set of alternatives. Alternatives are
+  separated by a "|" and all the alternatives are enclosed in "(" and
+  ")".
+
+Additional TAGS may follow as a comma separated set of the following
+tags enclosed in square brackets.
+
+* w -- Path is writable by the user. This capability is usually
+  limited to the control domain (e.g. dom0).
+* ARM | ARM32 | X86: the path is available for the respective architecture
+  only.
+* PV --  Path is valid for PV capable hypervisors only.
+* HVM -- Path is valid for HVM capable hypervisors only.
+* CONFIG_* -- Path is valid only in case the hypervisor was built with
+  the respective config option.
+
+## Example
+
+A populated Xen hypervisor file system might look like the following example:
+
+    /
+        buildinfo/           directory containing build-time data
+            config           contents of .config file used to build Xen
+        cpu-bugs/            x86: directory of cpu bug information
+            l1tf             "Vulnerable" or "Not vulnerable"
+            mds              "Vulnerable" or "Not vulnerable"
+            meltdown         "Vulnerable" or "Not vulnerable"
+            spec-store-bypass "Vulnerable" or "Not vulnerable"
+            spectre-v1       "Vulnerable" or "Not vulnerable"
+            spectre-v2       "Vulnerable" or "Not vulnerable"
+            mitigations/     directory of mitigation settings
+                bti-thunk    "N/A", "RETPOLINE", "LFENCE" or "JMP"
+                spec-ctrl    "No", "IBRS+" or IBRS-"
+                ibpb         "No" or "Yes"
+                l1d-flush    "No" or "Yes"
+                md-clear     "No" or "VERW"
+                l1tf-barrier "No" or "Yes"
+            active-hvm/      directory for mitigations active in hvm doamins
+                msr-spec-ctrl "No" or "Yes"
+                rsb          "No" or "Yes"
+                eager-fpu    "No" or "Yes"
+                md-clear     "No" or "Yes"
+            active-pv/       directory for mitigations active in pv doamins
+                msr-spec-ctrl "No" or "Yes"
+                rsb          "No" or "Yes"
+                eager-fpu    "No" or "Yes"
+                md-clear     "No" or "Yes"
+                xpti         "No" or list of "dom0", "domU", "PCID on"
+                l1tf-shadow  "No" or list of "dom0", "domU"
+        params/              directory with hypervisor parameter values
+                             (boot/runtime parameters)
+
+## General Paths
+
+#### /
+
+The root of the hypervisor file system.
-- 
2.16.4


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