libcrun: add ring buffer implementation

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

Makefile.am

@@ -35,6 +35,7 @@ endif
 check_LTLIBRARIES = libcrun_testing.la
 
 libcrun_SOURCES = src/libcrun/utils.c \
+		src/libcrun/ring_buffer.c \
 		src/libcrun/blake3/blake3.c \
 		src/libcrun/blake3/blake3_portable.c \
 		src/libcrun/cgroup-cgroupfs.c \
@@ -154,12 +155,12 @@ EXTRA_DIST = COPYING COPYING.libcrun README.md NEWS SECURITY.md rpm/crun.spec au
 	src/libcrun/handlers/handler-utils.h \
 	src/libcrun/linux.h src/libcrun/utils.h src/libcrun/error.h src/libcrun/criu.h \
 	src/libcrun/scheduler.h src/libcrun/status.h src/libcrun/terminal.h \
-	src/libcrun/mount_flags.h src/libcrun/intelrdt.h \
+	src/libcrun/mount_flags.h src/libcrun/intelrdt.h src/libcrun/ring_buffer.h \
 	crun.1.md crun.1 libcrun.lds \
 	krun.1.md krun.1 \
 	lua/luacrun.rockspec
 
-UNIT_TESTS = tests/tests_libcrun_utils tests/tests_libcrun_errors tests/tests_libcrun_intelrdt
+UNIT_TESTS = tests/tests_libcrun_utils tests/tests_libcrun_ring_buffer tests/tests_libcrun_errors tests/tests_libcrun_intelrdt
 
 if ENABLE_CRUN
 bin_PROGRAMS = crun
@@ -181,6 +182,11 @@ tests_tests_libcrun_utils_SOURCES = tests/tests_libcrun_utils.c
 tests_tests_libcrun_utils_LDADD = $(TESTS_LDADD)
 tests_tests_libcrun_utils_LDFLAGS = $(crun_LDFLAGS)
 
+tests_tests_libcrun_ring_buffer_CFLAGS = -I $(abs_top_builddir)/libocispec/src -I $(abs_top_srcdir)/libocispec/src -I $(abs_top_builddir)/src -I $(abs_top_srcdir)/src
+tests_tests_libcrun_ring_buffer_SOURCES = tests/tests_libcrun_ring_buffer.c
+tests_tests_libcrun_ring_buffer_LDADD = $(TESTS_LDADD)
+tests_tests_libcrun_ring_buffer_LDFLAGS = $(crun_LDFLAGS)
+
 tests_tests_libcrun_intelrdt_CFLAGS = -I $(abs_top_builddir)/libocispec/src -I $(abs_top_srcdir)/libocispec/src -I $(abs_top_builddir)/src -I $(abs_top_srcdir)/src
 tests_tests_libcrun_intelrdt_SOURCES = tests/tests_libcrun_intelrdt.c
 tests_tests_libcrun_intelrdt_LDADD = $(TESTS_LDADD)

src/libcrun/ring_buffer.c

@@ -0,0 +1,234 @@
+/*
+ * crun - OCI runtime written in C
+ *
+ * Copyright (C) 2024 Giuseppe Scrivano <giuseppe@scrivano.org>
+ * crun is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 of the License, or
+ * (at your option) any later version.
+ *
+ * crun is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with crun.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#define _GNU_SOURCE
+#include <config.h>
+#include <sys/uio.h>
+
+#include "ring_buffer.h"
+#include "utils.h"
+
+struct ring_buffer
+{
+  char *buffer;
+  size_t size;
+  size_t head;
+  size_t tail;
+};
+
+/*
+ * It returns up to two regions in `iov` that can be read from.
+ */
+static int
+ring_buffer_get_read_iov (struct ring_buffer *rb, struct iovec *iov)
+{
+  int iov_count = 0;
+
+  /* Buffer is empty.  */
+  if (rb->head == rb->tail)
+    return 0;
+
+  /* Head before tail.  There is only one region to read from, up to tail.  */
+  if (rb->tail > rb->head)
+    {
+      iov[iov_count].iov_base = rb->buffer + rb->head;
+      iov[iov_count].iov_len = rb->tail - rb->head;
+      iov_count++;
+    }
+  /* Head after tail.  There are two regions to read from, up to the
+   * end of the buffer and from the beginning of the buffer to tail.  */
+  else
+    {
+      iov[iov_count].iov_base = rb->buffer + rb->head;
+      iov[iov_count].iov_len = rb->size - rb->head;
+      iov_count++;
+
+      if (rb->tail > 0)
+        {
+          iov[iov_count].iov_base = rb->buffer;
+          iov[iov_count].iov_len = rb->tail;
+          iov_count++;
+        }
+    }
+  return iov_count;
+}
+
+/*
+ * It returns up to two regions in `iov` that can be written to without overwriting
+ * existing data.
+ */
+static int
+ring_buffer_get_write_iov (struct ring_buffer *rb, struct iovec *iov)
+{
+  int iov_count = 0;
+
+  /* Buffer is full.  */
+  if (rb->tail + 1 == rb->head)
+    return 0;
+
+  /* Tail before head.  There is only one region to write to, up to head.  */
+  if (rb->head > rb->tail + 1)
+    {
+      iov[iov_count].iov_base = rb->buffer + rb->tail;
+      iov[iov_count].iov_len = rb->head - rb->tail - 1;
+      iov_count++;
+    }
+  /* Tail after or equal to head.  There are two regions to write to, up to the
+   * end of the buffer and from the beginning of the buffer to head.  */
+  else
+    {
+      iov[iov_count].iov_base = rb->buffer + rb->tail;
+      iov[iov_count].iov_len = rb->size - rb->tail;
+      iov_count++;
+
+      if (rb->head > 1)
+        {
+          iov[iov_count].iov_base = rb->buffer;
+          iov[iov_count].iov_len = rb->head - 1;
+          iov_count++;
+        }
+    }
+  return iov_count;
+}
+
+/* manually advance the head after a successful read.  */
+static void
+ring_buffer_advance_nocheck_head (struct ring_buffer *rb, size_t amount)
+{
+  rb->head = (rb->head + amount) % rb->size;
+}
+
+/* manually advance the tail after a successful write.  */
+static void
+ring_buffer_advance_nocheck_tail (struct ring_buffer *rb, size_t amount)
+{
+  rb->tail = (rb->tail + amount) % rb->size;
+}
+
+size_t
+ring_buffer_get_data_available (struct ring_buffer *rb)
+{
+  if (rb->head <= rb->tail)
+    return rb->tail - rb->head;
+
+  return rb->size - rb->head + rb->tail;
+}
+
+size_t
+ring_buffer_get_size (struct ring_buffer *rb)
+{
+  return rb->size - 1;
+}
+
+size_t
+ring_buffer_get_space_available (struct ring_buffer *rb)
+{
+  return rb->size - ring_buffer_get_data_available (rb) - 1;
+}
+
+int
+ring_buffer_read (struct ring_buffer *rb, int fd, bool *is_eagain, libcrun_error_t *err)
+{
+  struct iovec iov[2];
+  int iov_count = 0;
+  ssize_t ret;
+
+  *is_eagain = false;
+
+  iov_count = ring_buffer_get_write_iov (rb, iov);
+  if (iov_count == 0)
+    {
+      *is_eagain = true;
+      return 0;
+    }
+
+  ret = readv (fd, iov, iov_count);
+  if (UNLIKELY (ret < 0))
+    {
+      if (errno == EIO)
+        return 0;
+      if (errno == EAGAIN || errno == EWOULDBLOCK)
+        {
+          *is_eagain = true;
+          return 0;
+        }
+      return crun_make_error (err, errno, "readv");
+    }
+  ring_buffer_advance_nocheck_tail (rb, ret);
+  return ret;
+}
+
+int
+ring_buffer_write (struct ring_buffer *rb, int fd, bool *is_eagain, libcrun_error_t *err)
+{
+  ssize_t ret;
+  struct iovec iov[2];
+  int iov_count = 0;
+
+  *is_eagain = false;
+
+  iov_count = ring_buffer_get_read_iov (rb, iov);
+  if (iov_count == 0)
+    {
+      *is_eagain = true;
+      return 0;
+    }
+
+  ret = writev (fd, iov, iov_count);
+  if (UNLIKELY (ret < 0))
+    {
+      if (errno == EIO)
+        return 0;
+      if (errno == EAGAIN || errno == EWOULDBLOCK)
+        {
+          *is_eagain = true;
+          return 0;
+        }
+      return crun_make_error (err, errno, "writev");
+    }
+  ring_buffer_advance_nocheck_head (rb, ret);
+  /* If the buffer is empty, reset the head and tail.  */
+  if (rb->head == rb->tail)
+    {
+      rb->head = 0;
+      rb->tail = 0;
+    }
+  return ret;
+}
+
+struct ring_buffer *
+ring_buffer_make (size_t size)
+{
+  struct ring_buffer *rb = xmalloc (sizeof (struct ring_buffer));
+
+  /* The extra byte is used to distinguish between full and empty buffer.  */
+  rb->size = size + 1;
+  rb->buffer = xmalloc (rb->size);
+  rb->head = 0;
+  rb->tail = 0;
+
+  return rb;
+}
+
+void
+ring_buffer_free (struct ring_buffer *rb)
+{
+  if (rb == NULL)
+    return;
+  free (rb->buffer);
+  free (rb);
+}

src/libcrun/ring_buffer.h

@@ -0,0 +1,52 @@
+/*
+ * crun - OCI runtime written in C
+ *
+ * Copyright (C) 2024 Giuseppe Scrivano <giuseppe@scrivano.org>
+ * crun is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 of the License, or
+ * (at your option) any later version.
+ *
+ * crun is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with crun.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef RING_BUFFER_H
+#define RING_BUFFER_H
+
+#include <config.h>
+
+#include "error.h"
+#include "utils.h"
+
+struct ring_buffer;
+
+size_t ring_buffer_get_data_available (struct ring_buffer *rb);
+
+size_t ring_buffer_get_space_available (struct ring_buffer *rb);
+
+size_t ring_buffer_get_size (struct ring_buffer *rb);
+
+int ring_buffer_read (struct ring_buffer *rb, int fd, bool *is_eagain, libcrun_error_t *err);
+
+int ring_buffer_write (struct ring_buffer *rb, int fd, bool *is_eagain, libcrun_error_t *err);
+
+struct ring_buffer *ring_buffer_make (size_t size);
+
+void ring_buffer_free (struct ring_buffer *rb);
+
+#define cleanup_ring_buffer __attribute__ ((cleanup (cleanup_ring_bufferp)))
+
+static inline void
+cleanup_ring_bufferp (struct ring_buffer **p)
+{
+  struct ring_buffer *rb = *p;
+  if (rb)
+    ring_buffer_free (rb);
+}
+
+#endif