From 6ff92c14b7a65f64dea4e0d4e8d19b2dcf3f57b3 Mon Sep 17 00:00:00 2001
From: msmith <msmith@FreeBSD.org>
Date: Tue, 5 Sep 2000 09:52:50 +0000
Subject: Implement readahead buffering for non-raw files.  This drastically
 improves the efficiency of byte-by-byte read operations on filesystems not
 already supported by the block cache (especially NFS).

This should be a welcome change for users booting via PXE, as the loader
now reads its startup files almost instantly, instead of taking tens of
seconds.
---
 lib/libstand/close.c | 50 ++++++++++++++++++-----------------
 lib/libstand/lseek.c | 65 ++++++++++++++++++++++++++-------------------
 lib/libstand/open.c  |  9 +++++++
 lib/libstand/read.c  | 75 +++++++++++++++++++++++++++++++++++++---------------
 lib/libstand/stand.h |  6 ++++-
 5 files changed, 132 insertions(+), 73 deletions(-)

(limited to 'lib/libstand')

diff --git a/lib/libstand/close.c b/lib/libstand/close.c
index aca6a65..bf81094 100644
--- a/lib/libstand/close.c
+++ b/lib/libstand/close.c
@@ -1,3 +1,4 @@
+/* $FreeBSD$ */
 /*	$NetBSD: close.c,v 1.7 1997/01/22 00:38:09 cgd Exp $	*/
 
 /*-
@@ -67,30 +68,31 @@
 #include "stand.h"
 
 int
-close(fd)
-	int fd;
+close(int fd)
 {
-	register struct open_file *f = &files[fd];
-	int err1 = 0, err2 = 0;
+    struct open_file	*f = &files[fd];
+    int			err1 = 0, err2 = 0;
 
-	if ((unsigned)fd >= SOPEN_MAX || f->f_flags == 0) {
-		errno = EBADF;
-		return (-1);
-	}
-	if (!(f->f_flags & F_RAW) && f->f_ops)
-		err1 = (f->f_ops->fo_close)(f);
-	if (!(f->f_flags & F_NODEV) && f->f_dev)
-		err2 = (f->f_dev->dv_close)(f);
-	if (f->f_devdata != NULL)
-		devclose(f);
-	f->f_flags = 0;
-	if (err1) {
-		errno = err1;
-		return (-1);
-	}
-	if (err2) {
-		errno = err2;
-		return (-1);
-	}
-	return (0);
+    if ((unsigned)fd >= SOPEN_MAX || f->f_flags == 0) {
+	errno = EBADF;
+	return (-1);
+    }
+    if (f->f_rabuf != NULL)
+	free(f->f_rabuf);
+    if (!(f->f_flags & F_RAW) && f->f_ops)
+	err1 = (f->f_ops->fo_close)(f);
+    if (!(f->f_flags & F_NODEV) && f->f_dev)
+	err2 = (f->f_dev->dv_close)(f);
+    if (f->f_devdata != NULL)
+	devclose(f);
+    f->f_flags = 0;
+    if (err1) {
+	errno = err1;
+	return (-1);
+    }
+    if (err2) {
+	errno = err2;
+	return (-1);
+    }
+    return (0);
 }
diff --git a/lib/libstand/lseek.c b/lib/libstand/lseek.c
index 0894912..91f8612 100644
--- a/lib/libstand/lseek.c
+++ b/lib/libstand/lseek.c
@@ -1,3 +1,4 @@
+/* $FreeBSD$ */
 /*	$NetBSD: lseek.c,v 1.4 1997/01/22 00:38:10 cgd Exp $	*/
 
 /*-
@@ -67,36 +68,46 @@
 #include "stand.h"
 
 off_t
-lseek(fd, offset, where)
-	int fd;
-	off_t offset;
-	int where;
+lseek(int fd, off_t offset, int where)
 {
-	register struct open_file *f = &files[fd];
+    struct open_file *f = &files[fd];
 
-	if ((unsigned)fd >= SOPEN_MAX || f->f_flags == 0) {
-		errno = EBADF;
-		return (-1);
-	}
+    if ((unsigned)fd >= SOPEN_MAX || f->f_flags == 0) {
+	errno = EBADF;
+	return (-1);
+    }
 
-	if (f->f_flags & F_RAW) {
-		/*
-		 * On RAW devices, update internal offset.
-		 */
-		switch (where) {
-		case SEEK_SET:
-			f->f_offset = offset;
-			break;
-		case SEEK_CUR:
-			f->f_offset += offset;
-			break;
-		case SEEK_END:
-		default:
-			errno = EOFFSET;
-			return (-1);
-		}
-		return (f->f_offset);
+    if (f->f_flags & F_RAW) {
+	/*
+	 * On RAW devices, update internal offset.
+	 */
+	switch (where) {
+	case SEEK_SET:
+	    f->f_offset = offset;
+	    break;
+	case SEEK_CUR:
+	    f->f_offset += offset;
+	    break;
+	case SEEK_END:
+	default:
+	    errno = EOFFSET;
+	    return (-1);
 	}
+	return (f->f_offset);
+    }
+
+    /*
+     * If this is a relative seek, we need to correct the offset for
+     * bytes that we have already read but the caller doesn't know
+     * about.
+     */
+    if (where == SEEK_CUR)
+	offset -= f->f_ralen;
+
+    /* 
+     * Invalidate the readahead buffer.
+     */
+    f->f_ralen = 0;
 
-	return (f->f_ops->fo_seek)(f, offset, where);
+    return (f->f_ops->fo_seek)(f, offset, where);
 }
diff --git a/lib/libstand/open.c b/lib/libstand/open.c
index 3a9127c..471f937 100644
--- a/lib/libstand/open.c
+++ b/lib/libstand/open.c
@@ -1,3 +1,4 @@
+/* $FreeBSD$ */
 /*	$NetBSD: open.c,v 1.16 1997/01/28 09:41:03 pk Exp $	*/
 
 /*-
@@ -79,6 +80,13 @@ o_gethandle(void)
     return(-1);
 }
 
+static void
+o_rainit(struct open_file *f)
+{
+    f->f_rabuf = malloc(SOPEN_RASIZE);
+    f->f_ralen = 0;
+    f->f_raoffset = 0;
+}
 
 int
 open(const char *fname, int mode)
@@ -118,6 +126,7 @@ open(const char *fname, int mode)
 	if (error == 0) {
 	    
 	    f->f_ops = file_system[i];
+	    o_rainit(f);
 	    return (fd);
 	}
 	if (error != EINVAL)
diff --git a/lib/libstand/read.c b/lib/libstand/read.c
index 5b14a75..28ff47e 100644
--- a/lib/libstand/read.c
+++ b/lib/libstand/read.c
@@ -1,3 +1,4 @@
+/* $FreeBSD$ */
 /*	$NetBSD: read.c,v 1.8 1997/01/22 00:38:12 cgd Exp $	*/
 
 /*-
@@ -68,29 +69,61 @@
 #include "stand.h"
 
 ssize_t
-read(fd, dest, bcount)
-	int fd;
-	void *dest;
-	size_t bcount;
+read(int fd, void *dest, size_t bcount)
 {
-	register struct open_file *f = &files[fd];
-	size_t resid;
+    struct open_file	*f = &files[fd];
+    size_t		resid;
 
-	if ((unsigned)fd >= SOPEN_MAX || !(f->f_flags & F_READ)) {
-		errno = EBADF;
-		return (-1);
+    if ((unsigned)fd >= SOPEN_MAX || !(f->f_flags & F_READ)) {
+	errno = EBADF;
+	return (-1);
+    }
+    if (f->f_flags & F_RAW) {
+	twiddle();
+	errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ,
+					btodb(f->f_offset), bcount, dest, &resid);
+	if (errno)
+	    return (-1);
+	f->f_offset += resid;
+	return (resid);
+    } 
+
+    /*
+     * Optimise reads from regular files using a readahead buffer.
+     * If the request can't be satisfied from the current buffer contents,
+     * check to see if it should be bypassed, or refill the buffer and complete
+     * the request.
+     */
+    resid = bcount;
+    for (;;) {
+	size_t	ccount, cresid;
+	/* how much can we supply? */
+	ccount = imin(f->f_ralen, resid);
+	if (ccount > 0) {
+	    bcopy(f->f_rabuf + f->f_raoffset, dest, ccount);
+	    f->f_raoffset += ccount;
+	    f->f_ralen -= ccount;
+	    resid -= ccount;
+	    if (resid == 0)
+		return(bcount);
+	    dest += ccount;
 	}
-	if (f->f_flags & F_RAW) {
-		twiddle();
-		errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ,
-			btodb(f->f_offset), bcount, dest, &resid);
-		if (errno)
-			return (-1);
-		f->f_offset += resid;
-		return (resid);
+
+	/* will filling the readahead buffer again not help? */
+	if (resid >= SOPEN_RASIZE) {
+	    /* bypass the rest of the request and leave the buffer empty */
+	    if ((errno = (f->f_ops->fo_read)(f, dest, resid, &cresid)))
+		return(bcount - resid);
+	    return(bcount - cresid);
 	}
-	resid = bcount;
-	if ((errno = (f->f_ops->fo_read)(f, dest, bcount, &resid)))
-		return (-1);
-	return (ssize_t)(bcount - resid);
+
+	/* fetch more data */
+	if ((errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, &cresid)))
+	    return(bcount - resid);	/* behave like fread() */
+	f->f_raoffset = 0;
+	f->f_ralen = SOPEN_RASIZE - cresid;
+	/* no more data, return what we had */
+	if (f->f_ralen == 0)
+	    return(bcount - resid);
+    }	
 }
diff --git a/lib/libstand/stand.h b/lib/libstand/stand.h
index aa8e65f..e48565a 100644
--- a/lib/libstand/stand.h
+++ b/lib/libstand/stand.h
@@ -159,7 +159,11 @@ struct open_file {
     void		*f_devdata;	/* device specific data */
     struct fs_ops	*f_ops;		/* pointer to file system operations */
     void		*f_fsdata;	/* file system specific data */
-    off_t		f_offset;	/* current file offset (F_RAW) */
+    off_t		f_offset;	/* current file offset */
+    char		*f_rabuf;	/* readahead buffer pointer */
+    size_t		f_ralen;	/* valid data in readahead buffer */
+    off_t		f_raoffset;	/* consumer offset in readahead buffer */
+#define SOPEN_RASIZE	512
 };
 
 #define	SOPEN_MAX	8
-- 
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