semihosting: Split out guestfd.c

In arm-compat-semi.c, we have more advanced treatment of
guest file descriptors than we do in other implementations.
Split out GuestFD and related functions to a new file so
that they can be shared.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/semihosting/guestfd.h

@@ -0,0 +1,83 @@
+/*
+ * Hosted file support for semihosting syscalls.
+ *
+ * Copyright (c) 2005, 2007 CodeSourcery.
+ * Copyright (c) 2019 Linaro
+ * Copyright © 2020 by Keith Packard <keithp@keithp.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#ifndef SEMIHOSTING_GUESTFD_H
+#define SEMIHOSTING_GUESTFD_H
+
+typedef enum GuestFDType {
+    GuestFDUnused = 0,
+    GuestFDHost = 1,
+    GuestFDGDB = 2,
+    GuestFDStatic = 3,
+} GuestFDType;
+
+/*
+ * Guest file descriptors are integer indexes into an array of
+ * these structures (we will dynamically resize as necessary).
+ */
+typedef struct GuestFD {
+    GuestFDType type;
+    union {
+        int hostfd;
+        struct {
+            const uint8_t *data;
+            size_t len;
+            size_t off;
+        } staticfile;
+    };
+} GuestFD;
+
+/**
+ * alloc_guestfd:
+ *
+ * Allocate an unused GuestFD index.  The associated guestfd index
+ * will still be GuestFDUnused until it is initialized.
+ */
+int alloc_guestfd(void);
+
+/**
+ * dealloc_guestfd:
+ * @guestfd: GuestFD index
+ *
+ * Deallocate a GuestFD index.  The associated GuestFD structure
+ * will be recycled for a subsequent allocation.
+ */
+void dealloc_guestfd(int guestfd);
+
+/**
+ * get_guestfd:
+ * @guestfd: GuestFD index
+ *
+ * Return the GuestFD structure associated with an initialized @guestfd,
+ * or NULL if it has not been allocated, or hasn't been initialized.
+ */
+GuestFD *get_guestfd(int guestfd);
+
+/**
+ * associate_guestfd:
+ * @guestfd: GuestFD index
+ * @hostfd: host file descriptor
+ *
+ * Initialize the GuestFD for @guestfd to GuestFDHost using @hostfd.
+ */
+void associate_guestfd(int guestfd, int hostfd);
+
+/**
+ * staticfile_guestfd:
+ * @guestfd: GuestFD index
+ * @data: data to be read
+ * @len: length of @data
+ *
+ * Initialize the GuestFD for @guestfd to GuestFDStatic.
+ * The @len bytes at @data will be returned to the guest on reads.
+ */
+void staticfile_guestfd(int guestfd, const uint8_t *data, size_t len);
+
+#endif /* SEMIHOSTING_GUESTFD_H */