This patch adds to libext2fs the ability to pre-fetch metadata
into the page cache in the hopes of speeding up libext2fs' clients.
There are two new library functions -- the first allows a client to
readahead a list of blocks, and the second is a helper function that
uses that first mechanism to load group data (bitmaps, inode tables).
e2fsck will employ both of these methods to speed itself up.
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
---
lib/ext2fs/Makefile.in | 4 +
lib/ext2fs/ext2fs.h | 13 +++
lib/ext2fs/readahead.c | 188 ++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 205 insertions(+)
create mode 100644 lib/ext2fs/readahead.c
diff --git a/lib/ext2fs/Makefile.in b/lib/ext2fs/Makefile.in
index 0c880c7..e64342e 100644
--- a/lib/ext2fs/Makefile.in
+++ b/lib/ext2fs/Makefile.in
@@ -78,6 +78,7 @@ OBJS= $(DEBUGFS_LIB_OBJS) $(RESIZE_LIB_OBJS) $(E2IMAGE_LIB_OBJS) \
qcow2.o \
read_bb.o \
read_bb_file.o \
+ readahead.o \
res_gdt.o \
rw_bitmaps.o \
swapfs.o \
@@ -155,6 +156,7 @@ SRCS= ext2_err.c \
$(srcdir)/qcow2.c \
$(srcdir)/read_bb.c \
$(srcdir)/read_bb_file.c \
+ $(srcdir)/readahead.c \
$(srcdir)/res_gdt.c \
$(srcdir)/rw_bitmaps.c \
$(srcdir)/swapfs.c \
@@ -903,6 +905,8 @@ read_bb_file.o: $(srcdir)/read_bb_file.c $(top_builddir)/lib/config.h \
$(srcdir)/ext2_fs.h $(srcdir)/ext3_extents.h $(top_srcdir)/lib/et/com_err.h \
$(srcdir)/ext2_io.h $(top_builddir)/lib/ext2fs/ext2_err.h \
$(srcdir)/ext2_ext_attr.h $(srcdir)/bitops.h
+readahead.o: $(srcdir)/readahead.c $(top_builddir)/lib/config.h \
+ $(srcdir)/ext2fs.h $(srcdir)/ext2_fs.h $(top_builddir)/lib/ext2fs/ext2_err.h
res_gdt.o: $(srcdir)/res_gdt.c $(top_builddir)/lib/config.h \
$(top_builddir)/lib/dirpaths.h $(srcdir)/ext2_fs.h \
$(top_builddir)/lib/ext2fs/ext2_types.h $(srcdir)/ext2fs.h \
diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
index 819a14a..933a14d 100644
--- a/lib/ext2fs/ext2fs.h
+++ b/lib/ext2fs/ext2fs.h
@@ -1563,6 +1563,19 @@ extern errcode_t ext2fs_read_bb_FILE(ext2_filsys fs, FILE *f,
void (*invalid)(ext2_filsys fs,
blk_t blk));
+/* readahead.c */
+#define EXT2_READA_SUPER (0x01)
+#define EXT2_READA_GDT (0x02)
+#define EXT2_READA_BBITMAP (0x04)
+#define EXT2_READA_IBITMAP (0x08)
+#define EXT2_READA_ITABLE (0x10)
+#define EXT2_READA_ALL_FLAGS (0x1F)
+errcode_t ext2fs_readahead(ext2_filsys fs, int flags, dgrp_t start,
+ dgrp_t ngroups);
+errcode_t ext2fs_readahead_dblist(ext2_filsys fs, int flags,
+ ext2_dblist dblist);
+int ext2fs_can_readahead(ext2_filsys fs);
+
/* res_gdt.c */
extern errcode_t ext2fs_create_resize_inode(ext2_filsys fs);
diff --git a/lib/ext2fs/readahead.c b/lib/ext2fs/readahead.c
new file mode 100644
index 0000000..ed6e555
--- /dev/null
+++ b/lib/ext2fs/readahead.c
@@ -0,0 +1,188 @@
+/*
+ * readahead.c -- Try to convince the OS to prefetch metadata.
+ *
+ * Copyright (C) 2014 Oracle.
+ *
+ * %Begin-Header%
+ * This file may be redistributed under the terms of the GNU Library
+ * General Public License, version 2.
+ * %End-Header%
+ */
+
+#include "config.h"
+#include <string.h>
+
+#include "ext2_fs.h"
+#include "ext2fs.h"
+
+#undef DEBUG
+
+#ifdef DEBUG
+# define dbg_printf(f, a...) do {printf(f, ## a); fflush(stdout); } while (0)
+#else
+# define dbg_printf(f, a...)
+#endif
+
+struct read_dblist {
+ errcode_t err;
+ blk64_t run_start;
+ blk64_t run_len;
+};
+
+static EXT2_QSORT_TYPE readahead_dir_block_cmp(const void *a, const void *b)
+{
+ const struct ext2_db_entry2 *db_a =
+ (const struct ext2_db_entry2 *) a;
+ const struct ext2_db_entry2 *db_b =
+ (const struct ext2_db_entry2 *) b;
+
+ return (int) (db_a->blk - db_b->blk);
+}
+
+static int readahead_dir_block(ext2_filsys fs, struct ext2_db_entry2 *db,
+ void *priv_data)
+{
+ errcode_t err = 0;
+ struct read_dblist *pr = priv_data;
+
+ if (!pr->run_len || db->blk != pr->run_start + pr->run_len) {
+ if (pr->run_len) {
+ pr->err = io_channel_cache_readahead(fs->io,
+ pr->run_start,
+ pr->run_len);
+ dbg_printf("readahead start=%llu len=%llu err=%d\n",
+ pr->run_start, pr->run_len,
+ (int)pr->err);
+ }
+ pr->run_start = db->blk;
+ pr->run_len = 0;
+ }
+ pr->run_len += db->blockcnt;
+
+ return pr->err ? DBLIST_ABORT : 0;
+}
+
+errcode_t ext2fs_readahead_dblist(ext2_filsys fs, int flags,
+ ext2_dblist dblist)
+{
+ errcode_t err;
+ struct read_dblist pr;
+
+ dbg_printf("%s: flags=0x%x\n", __func__, flags);
+ if (flags)
+ return EXT2_ET_INVALID_ARGUMENT;
+
+ ext2fs_dblist_sort2(dblist, readahead_dir_block_cmp);
+
+ memset(&pr, 0, sizeof(pr));
+ err = ext2fs_dblist_iterate2(dblist, readahead_dir_block, &pr);
+ if (pr.err)
+ return pr.err;
+ if (err)
+ return err;
+
+ if (pr.run_len)
+ err = io_channel_cache_readahead(fs->io, pr.run_start,
+ pr.run_len);
+
+ return err;
+}
+
+errcode_t ext2fs_readahead(ext2_filsys fs, int flags, dgrp_t start,
+ dgrp_t ngroups)
+{
+ blk64_t super, old_gdt, new_gdt;
+ blk_t blocks;
+ dgrp_t i;
+ ext2_dblist dblist;
+ dgrp_t end = start + ngroups;
+ errcode_t err = 0;
+
+ dbg_printf("%s: flags=0x%x start=%d groups=%d\n", __func__, flags,
+ start, ngroups);
+ if (flags & ~EXT2_READA_ALL_FLAGS)
+ return EXT2_ET_INVALID_ARGUMENT;
+
+ if (end > fs->group_desc_count)
+ end = fs->group_desc_count;
+
+ if (flags == 0)
+ return 0;
+
+ err = ext2fs_init_dblist(fs, &dblist);
+ if (err)
+ return err;
+
+ for (i = start; i < end; i++) {
+ err = ext2fs_super_and_bgd_loc2(fs, i, &super, &old_gdt,
+ &new_gdt, &blocks);
+ if (err)
+ break;
+
+ if (flags & EXT2_READA_SUPER) {
+ err = ext2fs_add_dir_block2(dblist, 0, super, 0);
+ if (err)
+ break;
+ }
+
+ if (flags & EXT2_READA_GDT) {
+ if (old_gdt)
+ err = ext2fs_add_dir_block2(dblist, 0, old_gdt,
+ blocks);
+ else if (new_gdt)
+ err = ext2fs_add_dir_block2(dblist, 0, new_gdt,
+ blocks);
+ else
+ err = 0;
+ if (err)
+ break;
+ }
+
+ if ((flags & EXT2_READA_BBITMAP) &&
+ !ext2fs_bg_flags_test(fs, i, EXT2_BG_BLOCK_UNINIT) &&
+ ext2fs_bg_free_blocks_count(fs, i) <
+ fs->super->s_blocks_per_group) {
+ super = ext2fs_block_bitmap_loc(fs, i);
+ err = ext2fs_add_dir_block2(dblist, 0, super, 1);
+ if (err)
+ break;
+ }
+
+ if ((flags & EXT2_READA_IBITMAP) &&
+ !ext2fs_bg_flags_test(fs, i, EXT2_BG_INODE_UNINIT) &&
+ ext2fs_bg_free_inodes_count(fs, i) <
+ fs->super->s_inodes_per_group) {
+ super = ext2fs_inode_bitmap_loc(fs, i);
+ err = ext2fs_add_dir_block2(dblist, 0, super, 1);
+ if (err)
+ break;
+ }
+
+ if ((flags & EXT2_READA_ITABLE) &&
+ ext2fs_bg_free_inodes_count(fs, i) <
+ fs->super->s_inodes_per_group) {
+ super = ext2fs_inode_table_loc(fs, i);
+ blocks = fs->inode_blocks_per_group -
+ (ext2fs_bg_itable_unused(fs, i) *
+ EXT2_INODE_SIZE(fs->super) / fs->blocksize);
+ err = ext2fs_add_dir_block2(dblist, 0, super, blocks);
+ if (err)
+ break;
+ }
+ }
+
+ if (!err)
+ err = ext2fs_readahead_dblist(fs, 0, dblist);
+
+ ext2fs_free_dblist(dblist);
+ return err;
+}
+
+int ext2fs_can_readahead(ext2_filsys fs)
+{
+ errcode_t err;
+
+ err = io_channel_cache_readahead(fs->io, 0, 1);
+ dbg_printf("%s: supp=%d\n", __func__, err != EXT2_ET_OP_NOT_SUPPORTED);
+ return err != EXT2_ET_OP_NOT_SUPPORTED;
+}
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