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authorMichael Pratt <mpratt@google.com>2018-07-12 10:36:16 -0700
committerShentubot <shentubot@google.com>2018-07-12 10:37:21 -0700
commit41e0b977e5ffc667750c0f706bb70173c5de2161 (patch)
tree0684cdc1122057eb8d2651943cfe513256d9e26c /pkg/sentry/kernel
parentb363799bd879a7c36a87bc4a91f5c45c91ad6473 (diff)
Format documentation
PiperOrigin-RevId: 204323728 Change-Id: I1ff9aa062ffa12583b2e38ec94c87db7a3711971
Diffstat (limited to 'pkg/sentry/kernel')
-rw-r--r--pkg/sentry/kernel/README.md80
1 files changed, 41 insertions, 39 deletions
diff --git a/pkg/sentry/kernel/README.md b/pkg/sentry/kernel/README.md
index 88760a9bb..427311be8 100644
--- a/pkg/sentry/kernel/README.md
+++ b/pkg/sentry/kernel/README.md
@@ -1,12 +1,12 @@
This package contains:
-- A (partial) emulation of the "core Linux kernel", which governs task
- execution and scheduling, system call dispatch, and signal handling. See
- below for details.
+- A (partial) emulation of the "core Linux kernel", which governs task
+ execution and scheduling, system call dispatch, and signal handling. See
+ below for details.
-- The top-level interface for the sentry's Linux kernel emulation in general,
- used by the `main` function of all versions of the sentry. This interface
- revolves around the `Env` type (defined in `kernel.go`).
+- The top-level interface for the sentry's Linux kernel emulation in general,
+ used by the `main` function of all versions of the sentry. This interface
+ revolves around the `Env` type (defined in `kernel.go`).
# Background
@@ -20,15 +20,15 @@ sentry's notion of a task unless otherwise specified.)
At a high level, Linux application threads can be thought of as repeating a "run
loop":
-- Some amount of application code is executed in userspace.
+- Some amount of application code is executed in userspace.
-- A trap (explicit syscall invocation, hardware interrupt or exception, etc.)
- causes control flow to switch to the kernel.
+- A trap (explicit syscall invocation, hardware interrupt or exception, etc.)
+ causes control flow to switch to the kernel.
-- Some amount of kernel code is executed in kernelspace, e.g. to handle the
- cause of the trap.
+- Some amount of kernel code is executed in kernelspace, e.g. to handle the
+ cause of the trap.
-- The kernel "returns from the trap" into application code.
+- The kernel "returns from the trap" into application code.
Analogously, each task in the sentry is associated with a *task goroutine* that
executes that task's run loop (`Task.run` in `task_run.go`). However, the
@@ -38,24 +38,25 @@ state to, and resuming execution from, checkpoints.
While in kernelspace, a Linux thread can be descheduled (cease execution) in a
variety of ways:
-- It can yield or be preempted, becoming temporarily descheduled but still
- runnable. At present, the sentry delegates scheduling of runnable threads to
- the Go runtime.
+- It can yield or be preempted, becoming temporarily descheduled but still
+ runnable. At present, the sentry delegates scheduling of runnable threads to
+ the Go runtime.
-- It can exit, becoming permanently descheduled. The sentry's equivalent is
- returning from `Task.run`, terminating the task goroutine.
+- It can exit, becoming permanently descheduled. The sentry's equivalent is
+ returning from `Task.run`, terminating the task goroutine.
-- It can enter interruptible sleep, a state in which it can be woken by a
- caller-defined wakeup or the receipt of a signal. In the sentry, interruptible
- sleep (which is ambiguously referred to as *blocking*) is implemented by
- making all events that can end blocking (including signal notifications)
- communicated via Go channels and using `select` to multiplex wakeup sources;
- see `task_block.go`.
+- It can enter interruptible sleep, a state in which it can be woken by a
+ caller-defined wakeup or the receipt of a signal. In the sentry,
+ interruptible sleep (which is ambiguously referred to as *blocking*) is
+ implemented by making all events that can end blocking (including signal
+ notifications) communicated via Go channels and using `select` to multiplex
+ wakeup sources; see `task_block.go`.
-- It can enter uninterruptible sleep, a state in which it can only be woken by a
- caller-defined wakeup. Killable sleep is a closely related variant in which
- the task can also be woken by SIGKILL. (These definitions also include Linux's
- "group-stopped" (`TASK_STOPPED`) and "ptrace-stopped" (`TASK_TRACED`) states.)
+- It can enter uninterruptible sleep, a state in which it can only be woken by
+ a caller-defined wakeup. Killable sleep is a closely related variant in
+ which the task can also be woken by SIGKILL. (These definitions also include
+ Linux's "group-stopped" (`TASK_STOPPED`) and "ptrace-stopped"
+ (`TASK_TRACED`) states.)
To maximize compatibility with Linux, sentry checkpointing appears as a spurious
signal-delivery interrupt on all tasks; interrupted system calls return `EINTR`
@@ -71,21 +72,22 @@ through sleeping operations.
We break the task's control flow graph into *states*, delimited by:
-1. Points where uninterruptible and killable sleeps may occur. For example,
-there exists a state boundary between signal dequeueing and signal delivery
-because there may be an intervening ptrace signal-delivery-stop.
+1. Points where uninterruptible and killable sleeps may occur. For example,
+ there exists a state boundary between signal dequeueing and signal delivery
+ because there may be an intervening ptrace signal-delivery-stop.
-2. Points where sleep-induced branches may "rejoin" normal execution. For
-example, the syscall exit state exists because it can be reached immediately
-following a synchronous syscall, or after a task that is sleeping in `execve()`
-or `vfork()` resumes execution.
+2. Points where sleep-induced branches may "rejoin" normal execution. For
+ example, the syscall exit state exists because it can be reached immediately
+ following a synchronous syscall, or after a task that is sleeping in
+ `execve()` or `vfork()` resumes execution.
-3. Points containing large branches. This is strictly for organizational
-purposes. For example, the state that processes interrupt-signaled conditions is
-kept separate from the main "app" state to reduce the size of the latter.
+3. Points containing large branches. This is strictly for organizational
+ purposes. For example, the state that processes interrupt-signaled
+ conditions is kept separate from the main "app" state to reduce the size of
+ the latter.
-4. `SyscallReinvoke`, which does not correspond to anything in Linux, and exists
-solely to serve the autosave feature.
+4. `SyscallReinvoke`, which does not correspond to anything in Linux, and
+ exists solely to serve the autosave feature.
![dot -Tpng -Goverlap=false -orun_states.png run_states.dot](g3doc/run_states.png "Task control flow graph")