[PATCH] First cut syslet async io support

[fio.git] / syslet.h

diff --git a/syslet.h b/syslet.h
new file mode 100644 (file)
index 0000000..85f0ebc
--- /dev/null
+++ b/syslet.h
@@ -0,0 +1,136 @@
+#ifndef _LINUX_SYSLET_H
+#define _LINUX_SYSLET_H
+/*
+ * The syslet subsystem - asynchronous syscall execution support.
+ *
+ * Started by Ingo Molnar:
+ *
+ *  Copyright (C) 2007 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
+ *
+ * User-space API/ABI definitions:
+ */
+
+/*
+ * This is the 'Syslet Atom' - the basic unit of execution
+ * within the syslet framework. A syslet always represents
+ * a single system-call plus its arguments, plus has conditions
+ * attached to it that allows the construction of larger
+ * programs from these atoms. User-space variables can be used
+ * (for example a loop index) via the special sys_umem*() syscalls.
+ *
+ * Arguments are implemented via pointers to arguments. This not
+ * only increases the flexibility of syslet atoms (multiple syslets
+ * can share the same variable for example), but is also an
+ * optimization: copy_uatom() will only fetch syscall parameters
+ * up until the point it meets the first NULL pointer. 50% of all
+ * syscalls have 2 or less parameters (and 90% of all syscalls have
+ * 4 or less parameters).
+ *
+ * [ Note: since the argument array is at the end of the atom, and the
+ *   kernel will not touch any argument beyond the final NULL one, atoms
+ *   might be packed more tightly. (the only special case exception to
+ *   this rule would be SKIP_TO_NEXT_ON_STOP atoms, where the kernel will
+ *   jump a full syslet_uatom number of bytes.) ]
+ */
+struct syslet_uatom {
+       unsigned long                           flags;
+       unsigned long                           nr;
+       long __user                             *ret_ptr;
+       struct syslet_uatom     __user          *next;
+       unsigned long           __user          *arg_ptr[6];
+       /*
+        * User-space can put anything in here, kernel will not
+        * touch it:
+        */
+       void __user                             *private;
+};
+
+/*
+ * Flags to modify/control syslet atom behavior:
+ */
+
+/*
+ * Immediately queue this syslet asynchronously - do not even
+ * attempt to execute it synchronously in the user context:
+ */
+#define SYSLET_ASYNC                           0x00000001
+
+/*
+ * Never queue this syslet asynchronously - even if synchronous
+ * execution causes a context-switching:
+ */
+#define SYSLET_SYNC                            0x00000002
+
+/*
+ * Do not queue the syslet in the completion ring when done.
+ *
+ * ( the default is that the final atom of a syslet is queued
+ *   in the completion ring. )
+ *
+ * Some syscalls generate implicit completion events of their
+ * own.
+ */
+#define SYSLET_NO_COMPLETE                     0x00000004
+
+/*
+ * Execution control: conditions upon the return code
+ * of the previous syslet atom. 'Stop' means syslet
+ * execution is stopped and the atom is put into the
+ * completion ring:
+ */
+#define SYSLET_STOP_ON_NONZERO                 0x00000008
+#define SYSLET_STOP_ON_ZERO                    0x00000010
+#define SYSLET_STOP_ON_NEGATIVE                        0x00000020
+#define SYSLET_STOP_ON_NON_POSITIVE            0x00000040
+
+#define SYSLET_STOP_MASK                               \
+       (       SYSLET_STOP_ON_NONZERO          |       \
+               SYSLET_STOP_ON_ZERO             |       \
+               SYSLET_STOP_ON_NEGATIVE         |       \
+               SYSLET_STOP_ON_NON_POSITIVE             )
+
+/*
+ * Special modifier to 'stop' handling: instead of stopping the
+ * execution of the syslet, the linearly next syslet is executed.
+ * (Normal execution flows along atom->next, and execution stops
+ *  if atom->next is NULL or a stop condition becomes true.)
+ *
+ * This is what allows true branches of execution within syslets.
+ */
+#define SYSLET_SKIP_TO_NEXT_ON_STOP            0x00000080
+
+/*
+ * This is the (per-user-context) descriptor of the async completion
+ * ring. This gets registered via sys_async_register().
+ */
+struct async_head_user {
+       /*
+        * Pointers to completed async syslets (i.e. syslets that
+        * generated a cachemiss and went async, returning -EASYNCSYSLET
+        * to the user context by sys_async_exec()) are queued here.
+        * Syslets that were executed synchronously are not queued here.
+        *
+        * Note: the final atom that generated the exit condition is
+        * queued here. Normally this would be the last atom of a syslet.
+        */
+       struct syslet_uatom __user              **completion_ring;
+       /*
+        * Ring size in bytes:
+        */
+       unsigned long                           ring_size_bytes;
+
+       /*
+        * Maximum number of asynchronous contexts the kernel creates.
+        *
+        * -1UL has a special meaning: the kernel manages the optimal
+        * size of the async pool.
+        *
+        * Note: this field should be valid for the lifetime of async
+        * processing, because future kernels detect changes to this
+        * field. (enabling user-space to control the size of the async
+        * pool in a low-overhead fashion)
+        */
+       unsigned long                           max_nr_threads;
+};
+
+#endif