Merge remote-tracking branch 'remotes/cschoenebeck/tags/pull-9p-20211027' into staging

9pfs: performance fix and cleanup

* First patch fixes suboptimal I/O performance on guest due to previously
  incorrect block size being transmitted to 9p client.

* Subsequent patches are cleanup ones intended to reduce code complexity.

* remotes/cschoenebeck/tags/pull-9p-20211027:
  9pfs: use P9Array in v9fs_walk()
  9pfs: make V9fsPath usable via P9Array API
  9pfs: make V9fsString usable via P9Array API
  fsdev/p9array.h: check scalar type in P9ARRAY_NEW()
  9pfs: introduce P9Array
  9pfs: simplify blksize_to_iounit()
  9pfs: deduplicate iounit code
  9pfs: fix wrong I/O block size in Rgetattr

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 160 insertions, 0 deletions

diff --git a/fsdev/p9array.h b/fsdev/p9array.h
new file mode 100644
index 0000000000..6aa25327ca
--- /dev/null
+++ b/fsdev/p9array.h
@@ -0,0 +1,160 @@
+/*
+ * P9Array - deep auto free C-array
+ *
+ * Copyright (c) 2021 Crudebyte
+ *
+ * Authors:
+ *   Christian Schoenebeck <qemu_oss@crudebyte.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef QEMU_P9ARRAY_H
+#define QEMU_P9ARRAY_H
+
+#include "qemu/compiler.h"
+
+/**
+ * P9Array provides a mechanism to access arrays in common C-style (e.g. by
+ * square bracket [] operator) in conjunction with reference variables that
+ * perform deep auto free of the array when leaving the scope of the auto
+ * reference variable. That means not only is the array itself automatically
+ * freed, but also memory dynamically allocated by the individual array
+ * elements.
+ *
+ * Example:
+ *
+ * Consider the following user struct @c Foo which shall be used as scalar
+ * (element) type of an array:
+ * @code
+ * typedef struct Foo {
+ *     int i;
+ *     char *s;
+ * } Foo;
+ * @endcode
+ * and assume it has the following function to free memory allocated by @c Foo
+ * instances:
+ * @code
+ * void free_foo(Foo *foo) {
+ *     free(foo->s);
+ * }
+ * @endcode
+ * Add the following to a shared header file:
+ * @code
+ * P9ARRAY_DECLARE_TYPE(Foo);
+ * @endcode
+ * and the following to a C unit file:
+ * @code
+ * P9ARRAY_DEFINE_TYPE(Foo, free_foo);
+ * @endcode
+ * Finally the array may then be used like this:
+ * @code
+ * void doSomething(size_t n) {
+ *     P9ARRAY_REF(Foo) foos = NULL;
+ *     P9ARRAY_NEW(Foo, foos, n);
+ *     for (size_t i = 0; i < n; ++i) {
+ *         foos[i].i = i;
+ *         foos[i].s = calloc(4096, 1);
+ *         snprintf(foos[i].s, 4096, "foo %d", i);
+ *         if (...) {
+ *             return; // array auto freed here
+ *         }
+ *     }
+ *     // array auto freed here
+ * }
+ * @endcode
+ */
+
+/**
+ * Declares an array type for the passed @a scalar_type.
+ *
+ * This is typically used from a shared header file.
+ *
+ * @param scalar_type - type of the individual array elements
+ */
+#define P9ARRAY_DECLARE_TYPE(scalar_type) \
+    typedef struct P9Array##scalar_type { \
+        size_t len; \
+        scalar_type first[]; \
+    } P9Array##scalar_type; \
+    \
+    void p9array_new_##scalar_type(scalar_type **auto_var, size_t len); \
+    void p9array_auto_free_##scalar_type(scalar_type **auto_var); \
+
+/**
+ * Defines an array type for the passed @a scalar_type and appropriate
+ * @a scalar_cleanup_func.
+ *
+ * This is typically used from a C unit file.
+ *
+ * @param scalar_type - type of the individual array elements
+ * @param scalar_cleanup_func - appropriate function to free memory dynamically
+ *                              allocated by individual array elements before
+ */
+#define P9ARRAY_DEFINE_TYPE(scalar_type, scalar_cleanup_func) \
+    void p9array_new_##scalar_type(scalar_type **auto_var, size_t len) \
+    { \
+        p9array_auto_free_##scalar_type(auto_var); \
+        P9Array##scalar_type *arr = g_malloc0(sizeof(P9Array##scalar_type) + \
+            len * sizeof(scalar_type)); \
+        arr->len = len; \
+        *auto_var = &arr->first[0]; \
+    } \
+    \
+    void p9array_auto_free_##scalar_type(scalar_type **auto_var) \
+    { \
+        scalar_type *first = (*auto_var); \
+        if (!first) { \
+            return; \
+        } \
+        P9Array##scalar_type *arr = (P9Array##scalar_type *) ( \
+            ((char *)first) - offsetof(P9Array##scalar_type, first) \
+        ); \
+        for (size_t i = 0; i < arr->len; ++i) { \
+            scalar_cleanup_func(&arr->first[i]); \
+        } \
+        g_free(arr); \
+    } \
+
+/**
+ * Used to declare a reference variable (unique pointer) for an array. After
+ * leaving the scope of the reference variable, the associated array is
+ * automatically freed.
+ *
+ * @param scalar_type - type of the individual array elements
+ */
+#define P9ARRAY_REF(scalar_type) \
+    __attribute((__cleanup__(p9array_auto_free_##scalar_type))) scalar_type*
+
+/**
+ * Allocates a new array of passed @a scalar_type with @a len number of array
+ * elements and assigns the created array to the reference variable
+ * @a auto_var.
+ *
+ * @param scalar_type - type of the individual array elements
+ * @param auto_var - destination reference variable
+ * @param len - amount of array elements to be allocated immediately
+ */
+#define P9ARRAY_NEW(scalar_type, auto_var, len) \
+    QEMU_BUILD_BUG_MSG( \
+        !__builtin_types_compatible_p(scalar_type, typeof(*auto_var)), \
+        "P9Array scalar type mismatch" \
+    ); \
+    p9array_new_##scalar_type((&auto_var), len)
+
+#endif /* QEMU_P9ARRAY_H */