[Qemu-devel] [PATCH v9 16/17] block/io_uring: adds fd registration

[Aarushi Mehta <mehta.aaru20@gmail.com>]

Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
---
 block/io_uring.c   | 107 ++++++++++++++++++++++++++++++++++++++++++++-
 block/trace-events |   1 +
 2 files changed, 107 insertions(+), 1 deletion(-)

diff --git a/block/io_uring.c b/block/io_uring.c
index 86f32e18a1..1553cd2e58 100644
--- a/block/io_uring.c
+++ b/block/io_uring.c
@@ -45,10 +45,16 @@ typedef struct LuringQueue {
     QSIMPLEQ_HEAD(, LuringAIOCB) submit_queue;
 } LuringQueue;
 
+typedef struct LuringFd {
+    int *fd_array;
+    GHashTable *fd_lookup;
+} LuringFd;
+
 typedef struct LuringState {
     AioContext *aio_context;
 
     struct io_uring ring;
+    LuringFd fd_reg;
 
     /* io queue for submit at batch.  Protected by AioContext lock. */
     LuringQueue io_q;
@@ -306,6 +312,94 @@ static int ioq_submit(LuringState *s)
     return ret;
 }
 
+/**
+ * luring_fd_register:
+ *
+ * Register file descriptors, see luring_fd_lookup
+ */
+static int luring_fd_register(struct io_uring *ring, LuringFd *fd_reg, int fd)
+{
+    int ret, nr;
+    GHashTable *lookup = fd_reg->fd_lookup;
+    nr = g_hash_table_size(lookup);
+
+    /* If adding new, API requires older registrations to be removed */
+    if (nr) {
+        /*
+         * See linux b19062a56726, register needs the ring mutex, any
+         * submission in progress will complete before unregistering begins
+         * and new ones will have to wait.
+         */
+        ret = io_uring_unregister_files(ring);
+        if (ret < 0) {
+            return ret;
+        }
+    }
+
+    fd_reg->fd_array = g_realloc_n(fd_reg->fd_array, nr + 1, sizeof(int));
+    fd_reg->fd_array[nr] = fd;
+
+    g_hash_table_insert(lookup, GINT_TO_POINTER(fd), GINT_TO_POINTER(nr));
+    trace_luring_fd_register(fd, nr);
+    return io_uring_register_files(ring, fd_reg->fd_array, nr + 1);
+}
+/**
+ * luring_fd_unregister:
+ *
+ * Unregisters file descriptors, TODO: error handling
+ */
+static void luring_fd_unregister(LuringState *s)
+{
+        io_uring_unregister_files(&s->ring);
+        g_hash_table_unref(s->fd_reg.fd_lookup);
+        g_free(s->fd_reg.fd_array);
+}
+
+/**
+ * luring_fd_lookup:
+ *
+ * Used to lookup fd index in registered array at submission time
+ * If the lookup table has not been created or the fd is not in the table,
+ * the fd is registered.
+ *
+ * If registration errors, the hash is cleared and the fd used directly
+ *
+ * Unregistering is done at luring_detach_aio_context
+ */
+static int luring_fd_lookup(LuringState *s, int fd)
+{
+    int ret;
+    void *index;
+    GHashTable *lookup;
+
+    if (!s->fd_reg.fd_lookup) {
+        s->fd_reg.fd_lookup = g_hash_table_new_full(g_direct_hash,
+                                                    g_direct_equal,
+                                                    g_free, g_free);
+        luring_fd_register(&s->ring, &s->fd_reg, fd);
+    }
+    lookup = s->fd_reg.fd_lookup;
+    index = g_hash_table_lookup(lookup, GINT_TO_POINTER(fd));
+
+    if (index < 0) {
+        ret = luring_fd_register(&s->ring, &s->fd_reg, fd);
+
+        if (ret < 0) {
+            if (ret == -ENOMEM || ret == -EMFILE ||
+                ret == -ENXIO) {
+                return ret;
+            } else {
+                /* Should not reach here */
+                g_hash_table_remove_all(lookup);
+                g_free(s->fd_reg.fd_array);
+                return ret;
+            }
+        }
+        index = g_hash_table_lookup(lookup, GINT_TO_POINTER(fd));
+    }
+    return GPOINTER_TO_INT(index);
+}
+
 void luring_io_plug(BlockDriverState *bs, LuringState *s)
 {
     trace_luring_io_plug(s);
@@ -337,9 +431,14 @@ void luring_io_unplug(BlockDriverState *bs, LuringState *s)
 static int luring_do_submit(int fd, LuringAIOCB *luringcb, LuringState *s,
                             uint64_t offset, int type)
 {
-    int ret;
+    int ret, fd_index;
     struct io_uring_sqe *sqes = &luringcb->sqeq;
 
+    fd_index = luring_fd_lookup(s, fd);
+    if (fd_index >= 0) {
+        fd = fd_index;
+    }
+
     switch (type) {
     case QEMU_AIO_WRITE:
         io_uring_prep_writev(sqes, fd, luringcb->qiov->iov,
@@ -357,7 +456,11 @@ static int luring_do_submit(int fd, LuringAIOCB *luringcb, LuringState *s,
                         __func__, type);
         abort();
     }
+
     io_uring_sqe_set_data(sqes, luringcb);
+    if (fd_index >= 0) {
+        io_uring_sqe_set_flags(sqes, IOSQE_FIXED_FILE);
+    }
 
     QSIMPLEQ_INSERT_TAIL(&s->io_q.submit_queue, luringcb, next);
     s->io_q.in_queue++;
@@ -383,6 +486,7 @@ int coroutine_fn luring_co_submit(BlockDriverState *bs, LuringState *s, int fd,
         .qiov       = qiov,
         .is_read    = (type == QEMU_AIO_READ),
     };
+
     trace_luring_co_submit(bs, s, &luringcb, fd, offset, qiov ? qiov->size : 0,
                            type);
     ret = luring_do_submit(fd, &luringcb, s, offset, type);
@@ -399,6 +503,7 @@ int coroutine_fn luring_co_submit(BlockDriverState *bs, LuringState *s, int fd,
 
 void luring_detach_aio_context(LuringState *s, AioContext *old_context)
 {
+    luring_fd_unregister(s);
     aio_set_fd_handler(old_context, s->ring.ring_fd, false, NULL, NULL, NULL,
                        s);
     qemu_bh_delete(s->completion_bh);
diff --git a/block/trace-events b/block/trace-events
index 66aaf8352b..13571aa182 100644
--- a/block/trace-events
+++ b/block/trace-events
@@ -71,6 +71,7 @@ luring_co_submit(void *bs, void *s, void *luringcb, int fd, uint64_t offset, siz
 luring_process_completion(void *s, void *aiocb, int ret) "LuringState %p luringcb %p ret %d"
 luring_io_uring_submit(void *s, int ret) "LuringState %p ret %d"
 luring_resubmit_short_read(void *s, void *luringcb, int nread) "LuringState %p luringcb %p nread %d"
+luring_fd_register(int fd, int index) "fd %d index %d"
 
 # qcow2.c
 qcow2_writev_start_req(void *co, int64_t offset, int bytes) "co %p offset 0x%" PRIx64 " bytes %d"
-- 
2.21.0