From 3e45a561ddfed71c4e377f3450d6e8e31c702c96 Mon Sep 17 00:00:00 2001
From: midipix <writeonce@midipix.org>
Date: Jul 22 2024 03:21:42 +0000
Subject: io interfaces: added tpax_io_range_read_ahead().


---

diff --git a/include/tpax/tpax.h b/include/tpax/tpax.h
index eef7092..66bef6d 100644
--- a/include/tpax/tpax.h
+++ b/include/tpax/tpax.h
@@ -211,6 +211,8 @@ tpax_api int  tpax_io_seek                  (struct tpax_driver_ctx *, off_t, in
 
 tpax_api int  tpax_io_range_read_next       (struct tpax_driver_ctx *, void *, size_t);
 
+tpax_api int  tpax_io_range_read_ahead      (struct tpax_driver_ctx *, void *, size_t);
+
 tpax_api int  tpax_io_create_memory_snapshot(const struct tpax_driver_ctx *, int, const char *,
                                              const struct stat *, void *);
 
diff --git a/project/common.mk b/project/common.mk
index 8d2dee3..04220ea 100644
--- a/project/common.mk
+++ b/project/common.mk
@@ -4,6 +4,7 @@ API_SRCS = \
 	src/driver/tpax_unit_ctx.c \
 	src/io/tpax_create_memory_snapshot.c \
 	src/io/tpax_create_tmpfs_snapshot.c \
+	src/io/tpax_io_read_ahead.c \
 	src/io/tpax_io_read_next.c \
 	src/io/tpax_io_seek.c \
 	src/logic/tpax_archive_enqueue.c \
diff --git a/src/io/tpax_io_read_ahead.c b/src/io/tpax_io_read_ahead.c
new file mode 100644
index 0000000..c92c08c
--- /dev/null
+++ b/src/io/tpax_io_read_ahead.c
@@ -0,0 +1,75 @@
+/**************************************************************/
+/*  tpax: a topological pax implementation                    */
+/*  Copyright (C) 2020--2024  SysDeer Technologies, LLC       */
+/*  Released under GPLv2 and GPLv3; see COPYING.TPAX.         */
+/**************************************************************/
+
+#include <stdint.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
+
+#include <tpax/tpax.h>
+#include <tpax/tpax_specs.h>
+#include "tpax_driver_impl.h"
+#include "tpax_errinfo_impl.h"
+
+#define TPAX_IO_READ_MAX (2147483647)
+
+static int tpax_io_range_read_ahead_fileio(
+	struct tpax_driver_ctx *    dctx,
+	void *                      buf,
+	size_t                      size)
+{
+	int     fdin;
+	ssize_t nbytes;
+	off_t   cpos;
+
+	fdin = tpax_driver_fdin(dctx);
+	cpos = tpax_get_driver_cpos(dctx);
+
+	nbytes = pread(fdin,buf,size,cpos);
+
+	while ((nbytes < 0) && (errno = EINTR))
+		nbytes = pread(fdin,buf,size,cpos);
+
+	return nbytes;
+}
+
+static int tpax_io_range_read_ahead_mapped(
+	struct tpax_driver_ctx *    dctx,
+	void *                      buf,
+	size_t                      size)
+{
+	struct tpax_driver_ctx_impl * ictx;
+	char *                        ch;
+	off_t                         cpos;
+
+	ictx = tpax_get_driver_ictx(dctx);
+	cpos = tpax_get_driver_cpos(dctx);
+	size = (cpos + size <= ictx->mapsize) ? size : ictx->mapsize - cpos;
+
+	ch = ictx->mapaddr;
+	ch = &ch[cpos];
+
+	memcpy(buf,ch,size);
+
+	return size;
+}
+
+int tpax_io_range_read_ahead(struct tpax_driver_ctx * dctx, void * buf, size_t size)
+{
+	size = (size <= TPAX_IO_READ_MAX) ? size : TPAX_IO_READ_MAX;
+
+	if (dctx->cctx->srcflags & TPAX_SOURCE_DATA_FILEIO) {
+		return tpax_io_range_read_ahead_fileio(dctx,buf,size);
+
+	} else if (dctx->cctx->srcflags & TPAX_SOURCE_DATA_MAPPED) {
+		return tpax_io_range_read_ahead_mapped(dctx,buf,size);
+
+	}
+
+	return TPAX_CUSTOM_ERROR(
+		dctx,
+		TPAX_ERR_FLOW_ERROR);
+}