1 files changed, 75 insertions, 0 deletions
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);
+}