ext2fs: Add Direct I/O support to the ext2fs library
This adds the basic support for Direct I/O to unix_io.c, and adds a
new flag EXT_FLAG_DIRECT_IO which can be passed to ext2fs_open() or
ext2fs_open2() to request Direct I/O support.
Note that device mapper devices in Linux don't support Direct I/O, and
in some circumstances using Direct I/O can actually make performance
*worse*!
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c
index 78a1d1c..1df1fdd 100644
--- a/lib/ext2fs/unix_io.c
+++ b/lib/ext2fs/unix_io.c
@@ -17,6 +17,7 @@
#define _LARGEFILE_SOURCE
#define _LARGEFILE64_SOURCE
+#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
@@ -47,10 +48,16 @@
#include <sys/resource.h>
#endif
-#if defined(__linux__) && defined(_IO) && !defined(BLKGETSIZE)
+#if defined(__linux__) && defined(_IO) && !defined(BLKROGET)
#define BLKROGET _IO(0x12, 94) /* Get read-only status (0 = read_write). */
#endif
+#if defined(__linux__) && defined(_IO) && !defined(BLKSSZGET)
+#define BLKSSZGET _IO(0x12,104)/* get block device sector size */
+#endif
+
+#undef ALIGN_DEBUG
+
#include "ext2_fs.h"
#include "ext2fs.h"
@@ -77,12 +84,17 @@
int magic;
int dev;
int flags;
+ int align;
int access_time;
ext2_loff_t offset;
struct unix_cache cache[CACHE_SIZE];
+ void *bounce;
struct struct_io_stats io_stats;
};
+#define IS_ALIGNED(n, align) ((((unsigned long) n) & \
+ ((unsigned long) ((align)-1))) == 0)
+
static errcode_t unix_open(const char *name, int flags, io_channel *channel);
static errcode_t unix_close(io_channel channel);
static errcode_t unix_set_blksize(io_channel channel, int blksize);
@@ -104,14 +116,6 @@
static errcode_t unix_write_blk64(io_channel channel, unsigned long long block,
int count, const void *data);
-/* __FreeBSD_kernel__ is defined by GNU/kFreeBSD - the FreeBSD kernel
- * does not know buffered block devices - everything is raw. */
-#if defined(__CYGWIN__) || defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
-#define NEED_BOUNCE_BUFFER
-#else
-#undef NEED_BOUNCE_BUFFER
-#endif
-
static struct struct_io_manager struct_unix_manager = {
EXT2_ET_MAGIC_IO_MANAGER,
"Unix I/O Manager",
@@ -121,11 +125,7 @@
unix_read_blk,
unix_write_blk,
unix_flush,
-#ifdef NEED_BOUNCE_BUFFER
- 0,
-#else
unix_write_byte,
-#endif
unix_set_option,
unix_get_stats,
unix_read_blk64,
@@ -153,7 +153,6 @@
/*
* Here are the raw I/O functions
*/
-#ifndef NEED_BOUNCE_BUFFER
static errcode_t raw_read_blk(io_channel channel,
struct unix_private_data *data,
unsigned long long block,
@@ -171,12 +170,38 @@
retval = errno ? errno : EXT2_ET_LLSEEK_FAILED;
goto error_out;
}
- actual = read(data->dev, buf, size);
- if (actual != size) {
- if (actual < 0)
- actual = 0;
- retval = EXT2_ET_SHORT_READ;
- goto error_out;
+ if ((data->align == 0) ||
+ ((IS_ALIGNED(buf, data->align)) && IS_ALIGNED(size, data->align))) {
+ actual = read(data->dev, buf, size);
+ if (actual != size) {
+ short_read:
+ if (actual < 0)
+ actual = 0;
+ retval = EXT2_ET_SHORT_READ;
+ goto error_out;
+ }
+ return 0;
+ }
+
+#ifdef ALIGN_DEBUG
+ printf("raw_read_blk: O_DIRECT fallback: %p %lu\n", buf,
+ (unsigned long) size);
+#endif
+
+ /*
+ * The buffer or size which we're trying to read isn't aligned
+ * to the O_DIRECT rules, so we need to do this the hard way...
+ */
+ while (size > 0) {
+ actual = read(data->dev, data->bounce, channel->block_size);
+ if (actual != channel->block_size)
+ goto short_read;
+ actual = size;
+ if (size > channel->block_size)
+ actual = channel->block_size;
+ memcpy(buf, data->bounce, actual);
+ size -= actual;
+ buf += actual;
}
return 0;
@@ -187,61 +212,6 @@
size, actual, retval);
return retval;
}
-#else /* NEED_BOUNCE_BUFFER */
-/*
- * Windows and FreeBSD block devices only allow sector alignment IO in offset and size
- */
-static errcode_t raw_read_blk(io_channel channel,
- struct unix_private_data *data,
- unsigned long block,
- int count, void *buf)
-{
- errcode_t retval;
- size_t size, alignsize, fragment;
- ext2_loff_t location;
- int total = 0, actual;
-#define BLOCKALIGN 512
- char sector[BLOCKALIGN];
-
- size = (count < 0) ? -count : count * channel->block_size;
- data->io_stats.bytes_read += size;
- location = ((ext2_loff_t) block * channel->block_size) + data->offset;
-#ifdef DEBUG
- printf("count=%d, size=%d, block=%lu, blk_size=%d, location=%llx\n",
- count, size, block, channel->block_size, (long long)location);
-#endif
- if (ext2fs_llseek(data->dev, location, SEEK_SET) != location) {
- retval = errno ? errno : EXT2_ET_LLSEEK_FAILED;
- goto error_out;
- }
- fragment = size % BLOCKALIGN;
- alignsize = size - fragment;
- if (alignsize) {
- actual = read(data->dev, buf, alignsize);
- if (actual != alignsize)
- goto short_read;
- }
- if (fragment) {
- actual = read(data->dev, sector, BLOCKALIGN);
- if (actual != BLOCKALIGN)
- goto short_read;
- memcpy(buf+alignsize, sector, fragment);
- }
- return 0;
-
-short_read:
- if (actual>0)
- total += actual;
- retval = EXT2_ET_SHORT_READ;
-
-error_out:
- memset((char *) buf+total, 0, size-actual);
- if (channel->read_error)
- retval = (channel->read_error)(channel, block, count, buf,
- size, actual, retval);
- return retval;
-}
-#endif
static errcode_t raw_write_blk(io_channel channel,
struct unix_private_data *data,
@@ -269,10 +239,43 @@
goto error_out;
}
- actual = write(data->dev, buf, size);
- if (actual != size) {
- retval = EXT2_ET_SHORT_WRITE;
- goto error_out;
+ if ((data->align == 0) ||
+ ((IS_ALIGNED(buf, data->align)) && IS_ALIGNED(size, data->align))) {
+ actual = write(data->dev, buf, size);
+ if (actual != size) {
+ short_write:
+ retval = EXT2_ET_SHORT_WRITE;
+ goto error_out;
+ }
+ return 0;
+ }
+
+#ifdef ALIGN_DEBUG
+ printf("raw_write_blk: O_DIRECT fallback: %p %lu\n", buf,
+ (unsigned long) size);
+#endif
+ /*
+ * The buffer or size which we're trying to write isn't aligned
+ * to the O_DIRECT rules, so we need to do this the hard way...
+ */
+ while (size > 0) {
+ if (size < channel->block_size) {
+ actual = read(data->dev, data->bounce,
+ channel->block_size);
+ if (actual != channel->block_size) {
+ retval = EXT2_ET_SHORT_READ;
+ goto error_out;
+ }
+ }
+ actual = size;
+ if (size > channel->block_size)
+ actual = channel->block_size;
+ memcpy(data->bounce, buf, actual);
+ actual = write(data->dev, data->bounce, channel->block_size);
+ if (actual != channel->block_size)
+ goto short_write;
+ size -= actual;
+ buf += actual;
}
return 0;
@@ -304,11 +307,18 @@
cache->in_use = 0;
if (cache->buf)
ext2fs_free_mem(&cache->buf);
- if ((retval = ext2fs_get_mem(channel->block_size,
- &cache->buf)))
+ retval = ext2fs_get_memalign(channel->block_size,
+ data->align, &cache->buf);
+ if (retval)
return retval;
}
- return 0;
+ if (data->align) {
+ if (data->bounce)
+ ext2fs_free_mem(&data->bounce);
+ retval = ext2fs_get_memalign(channel->block_size, data->align,
+ &data->bounce);
+ }
+ return retval;
}
/* Free the cache buffers */
@@ -325,8 +335,9 @@
cache->in_use = 0;
if (cache->buf)
ext2fs_free_mem(&cache->buf);
- cache->buf = 0;
}
+ if (data->bounce)
+ ext2fs_free_mem(&data->bounce);
}
#ifndef NO_IO_CACHE
@@ -449,12 +460,13 @@
data->magic = EXT2_ET_MAGIC_UNIX_IO_CHANNEL;
data->io_stats.num_fields = 2;
- if ((retval = alloc_cache(io, data)))
- goto cleanup;
-
open_flags = (flags & IO_FLAG_RW) ? O_RDWR : O_RDONLY;
if (flags & IO_FLAG_EXCLUSIVE)
open_flags |= O_EXCL;
+ if (flags & IO_FLAG_DIRECT_IO)
+ open_flags |= O_DIRECT;
+ data->flags = flags;
+
#ifdef HAVE_OPEN64
data->dev = open64(io->name, open_flags);
#else
@@ -465,6 +477,25 @@
goto cleanup;
}
+#ifdef BLKSSZGET
+ if (flags & IO_FLAG_DIRECT_IO) {
+ if (ioctl(data->dev, BLKSSZGET, &data->align) != 0)
+ data->align = io->block_size;
+ }
+#endif
+
+#if defined(__CYGWIN__) || defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
+ /*
+ * Some operating systems require that the buffers be aligned,
+ * regardless of O_DIRECT
+ */
+ data->align = 512;
+#endif
+
+
+ if ((retval = alloc_cache(io, data)))
+ goto cleanup;
+
#ifdef BLKROGET
if (flags & IO_FLAG_RW) {
int error;
@@ -617,6 +648,22 @@
cp += channel->block_size;
continue;
}
+ if (count == 1) {
+ /*
+ * Special case where we read directly into the
+ * cache buffer; important in the O_DIRECT case
+ */
+ cache = reuse[0];
+ reuse_cache(channel, data, cache, block);
+ if ((retval = raw_read_blk(channel, data, block, 1,
+ cache->buf))) {
+ cache->in_use = 0;
+ return retval;
+ }
+ memcpy(cp, cache->buf, channel->block_size);
+ return 0;
+ }
+
/*
* Find the number of uncached blocks so we can do a
* single read request
@@ -718,6 +765,13 @@
data = (struct unix_private_data *) channel->private_data;
EXT2_CHECK_MAGIC(data, EXT2_ET_MAGIC_UNIX_IO_CHANNEL);
+ if (data->align != 0) {
+#ifdef ALIGN_DEBUG
+ printf("unix_write_byte: O_DIRECT fallback\n");
+#endif
+ return EXT2_ET_UNIMPLEMENTED;
+ }
+
#ifndef NO_IO_CACHE
/*
* Flush out the cache completely