This patch extends functionality of e{2|4}fsprogs to add
EXT2_FLAG_DIRECT flag to be passed to ext2fs_open2() function. This
internally calls open() function with O_DIRECT and handles the memory
alignment for both read and write operations.
In some cases direct access to devices is necessary and that was the
main reason for this patch to be done.
The main reason why this was done is that pygrub (used by xen
virtualization user-space package, it's a python version of grub for
paravirtualized guests) sometimes uses outdated version of grub.conf
file. Modifications to xen package were *not* enough because e2fsprogs
doesn't open the files directly. That's why I added EXT2_FLAG_DIRECT
support to make read/write operations work directly when passed. It's
been tested with pygrub like mentioned above for read operation and it's
working fine.
Signed-off-by: Michal Novotny <minovotn@xxxxxxxxxx>
Author: Michal Novotny <minovotn@xxxxxxxxxx>
Date: Wed Dec 23 11:25:40 2009 +0200
extend e{2|4}fsprogs functionality to add EXT2_FLAG_DIRECT option
This patch extends functionality of e{2|4}fsprogs to add EXT2_FLAG_DIRECT
flag to be passed to ext2fs_open2() function. This internally calls open()
function with O_DIRECT and handles the memory alignment for both read and
write operations.
In some cases direct access to devices is necessary and that was the main
reason for this patch to be done.
Signed-off-by: Michal Novotny <minovotn@xxxxxxxxxx>
diff -up e2fsprogs-1.41.9/lib/ext2fs/ext2fs.h.opendirect e2fsprogs-1.41.9/lib/ext2fs/ext2fs.h
--- e2fsprogs-1.41.9/lib/ext2fs/ext2fs.h.opendirect 2009-12-23 10:04:05.000000000 +0100
+++ e2fsprogs-1.41.9/lib/ext2fs/ext2fs.h 2009-12-23 10:04:05.000000000 +0100
@@ -172,6 +172,7 @@ typedef struct ext2_file *ext2_file_t;
#define EXT2_FLAG_EXCLUSIVE 0x4000
#define EXT2_FLAG_SOFTSUPP_FEATURES 0x8000
#define EXT2_FLAG_NOFREE_ON_ERROR 0x10000
+#define EXT2_FLAG_DIRECT 0x20000
/*
* Special flag in the ext2 inode i_flag field that means that this is
diff -up e2fsprogs-1.41.9/lib/ext2fs/ext2_io.h.opendirect e2fsprogs-1.41.9/lib/ext2fs/ext2_io.h
--- e2fsprogs-1.41.9/lib/ext2fs/ext2_io.h.opendirect 2009-08-23 04:44:35.000000000 +0200
+++ e2fsprogs-1.41.9/lib/ext2fs/ext2_io.h 2009-12-23 10:04:05.000000000 +0100
@@ -29,6 +29,7 @@ typedef struct struct_io_channel *io_cha
typedef struct struct_io_stats *io_stats;
#define CHANNEL_FLAGS_WRITETHROUGH 0x01
+#define CHANNEL_FLAGS_DIRECT 0x02
struct struct_io_channel {
errcode_t magic;
@@ -88,6 +89,7 @@ struct struct_io_manager {
#define IO_FLAG_RW 0x0001
#define IO_FLAG_EXCLUSIVE 0x0002
+#define IO_FLAG_DIRECT 0x0004
/*
* Convenience functions....
diff -up e2fsprogs-1.41.9/lib/ext2fs/openfs.c.opendirect e2fsprogs-1.41.9/lib/ext2fs/openfs.c
--- e2fsprogs-1.41.9/lib/ext2fs/openfs.c.opendirect 2009-08-23 04:44:35.000000000 +0200
+++ e2fsprogs-1.41.9/lib/ext2fs/openfs.c 2009-12-23 10:04:05.000000000 +0100
@@ -121,6 +121,8 @@ errcode_t ext2fs_open2(const char *name,
io_flags |= IO_FLAG_RW;
if (flags & EXT2_FLAG_EXCLUSIVE)
io_flags |= IO_FLAG_EXCLUSIVE;
+ if (flags & EXT2_FLAG_DIRECT)
+ io_flags |= IO_FLAG_DIRECT;
retval = manager->open(fs->device_name, io_flags, &fs->io);
if (retval)
goto cleanup;
@@ -296,6 +298,7 @@ errcode_t ext2fs_open2(const char *name,
}
fs->desc_blocks = ext2fs_div_ceil(fs->group_desc_count,
EXT2_DESC_PER_BLOCK(fs->super));
+
retval = ext2fs_get_array(fs->desc_blocks, fs->blocksize,
&fs->group_desc);
if (retval)
diff -up e2fsprogs-1.41.9/lib/ext2fs/unix_io.c.opendirect e2fsprogs-1.41.9/lib/ext2fs/unix_io.c
--- e2fsprogs-1.41.9/lib/ext2fs/unix_io.c.opendirect 2009-08-13 03:39:57.000000000 +0200
+++ e2fsprogs-1.41.9/lib/ext2fs/unix_io.c 2009-12-23 10:16:26.000000000 +0100
@@ -17,6 +17,7 @@
#define _LARGEFILE_SOURCE
#define _LARGEFILE64_SOURCE
+#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
@@ -163,15 +164,37 @@ static errcode_t raw_read_blk(io_channel
ssize_t size;
ext2_loff_t location;
int actual = 0;
+ int memret;
+ void *aligned_buffer;
+ long pagesize;
size = (count < 0) ? -count : count * channel->block_size;
+
data->io_stats.bytes_read += size;
location = ((ext2_loff_t) block * channel->block_size) + data->offset;
if (ext2fs_llseek(data->dev, location, SEEK_SET) != location) {
retval = errno ? errno : EXT2_ET_LLSEEK_FAILED;
goto error_out;
}
- actual = read(data->dev, buf, size);
+
+ if (channel->flags & CHANNEL_FLAGS_DIRECT) {
+ pagesize = sysconf(_SC_PAGE_SIZE);
+ if (pagesize < 0)
+ goto error_out;
+
+ memret = posix_memalign(&aligned_buffer, pagesize, size);
+ if (memret != 0) {
+ errno = memret;
+ goto error_out;
+ }
+ actual = read(data->dev, aligned_buffer, size);
+ if (actual > 0)
+ memcpy(buf, aligned_buffer, size);
+ free(aligned_buffer);
+ }
+ else
+ actual = read(data->dev, buf, size);
+
if (actual != size) {
if (actual < 0)
actual = 0;
@@ -252,6 +275,9 @@ static errcode_t raw_write_blk(io_channe
ext2_loff_t location;
int actual = 0;
errcode_t retval;
+ int memret;
+ void *aligned_buffer;
+ long pagesize;
if (count == 1)
size = channel->block_size;
@@ -269,7 +295,23 @@ static errcode_t raw_write_blk(io_channe
goto error_out;
}
- actual = write(data->dev, buf, size);
+ if (channel->flags & CHANNEL_FLAGS_DIRECT) {
+ pagesize = sysconf(_SC_PAGE_SIZE);
+ if (pagesize < 0)
+ goto error_out;
+
+ memret = posix_memalign(&aligned_buffer, pagesize, size);
+ if (memret != 0) {
+ errno = memret;
+ goto error_out;
+ }
+ memcpy(aligned_buffer, buf, size);
+ actual = write(data->dev, aligned_buffer, size);
+ free(aligned_buffer);
+ }
+ else
+ actual = write(data->dev, buf, size);
+
if (actual != size) {
retval = EXT2_ET_SHORT_WRITE;
goto error_out;
@@ -443,6 +485,9 @@ static errcode_t unix_open(const char *n
io->write_error = 0;
io->refcount = 1;
+ if (flags & IO_FLAG_DIRECT)
+ io->flags = CHANNEL_FLAGS_DIRECT;
+
memset(data, 0, sizeof(struct unix_private_data));
data->magic = EXT2_ET_MAGIC_UNIX_IO_CHANNEL;
data->io_stats.num_fields = 2;
@@ -453,6 +498,8 @@ static errcode_t unix_open(const char *n
open_flags = (flags & IO_FLAG_RW) ? O_RDWR : O_RDONLY;
if (flags & IO_FLAG_EXCLUSIVE)
open_flags |= O_EXCL;
+ if (flags & IO_FLAG_DIRECT)
+ open_flags |= O_DIRECT;
#ifdef HAVE_OPEN64
data->dev = open64(io->name, open_flags);
#else
