On Tue, Nov 13, 2012 at 11:07:57PM -0500, George Spelvin wrote:
> When dumping a file with some messed-up block pointers, I discovered
> that I had a huge, and fully allocated destination file. (ls -s on the
> dump displayed some very large number, even though the original file
> only had about 8 blocks allocated.)
>
> It wouldprobably make more sense to seek over the gaps to create a
> sparse file.
Hi George,
Would you like to try this patch?
Thanks,
- Zheng
Subject: [PATCH] debugfs: dump a sparse file as a new sparse file
From: Zheng Liu <wenqing.lz@xxxxxxxxxx>
For dumping a sparse file ext2fs_file_read2() is defined to expand the
interface. It returns the size of hole and we can call lseek64(2) to skip it.
Signed-off-by: Zheng Liu <wenqing.lz@xxxxxxxxxx>
---
debugfs/dump.c | 16 ++++++++++++++--
lib/ext2fs/ext2fs.h | 3 +++
lib/ext2fs/fileio.c | 48 +++++++++++++++++++++++++++++++++++++-----------
3 files changed, 54 insertions(+), 13 deletions(-)
diff --git a/debugfs/dump.c b/debugfs/dump.c
index a15a0b7..013c0c8 100644
--- a/debugfs/dump.c
+++ b/debugfs/dump.c
@@ -105,10 +105,11 @@ static void dump_file(const char *cmdname, ext2_ino_t ino, int fd,
{
errcode_t retval;
struct ext2_inode inode;
- char buf[8192];
+ char buf[current_fs->blocksize];
ext2_file_t e2_file;
int nbytes;
unsigned int got;
+ ext2_off64_t seek;
if (debugfs_read_inode(ino, &inode, cmdname))
return;
@@ -119,11 +120,22 @@ static void dump_file(const char *cmdname, ext2_ino_t ino, int fd,
return;
}
while (1) {
- retval = ext2fs_file_read(e2_file, buf, sizeof(buf), &got);
+ if (fd == 1)
+ retval = ext2fs_file_read(e2_file, buf, sizeof(buf),
+ &got);
+ else
+ retval = ext2fs_file_read2(e2_file, buf, sizeof(buf),
+ &got, &seek);
if (retval)
com_err(cmdname, retval, "while reading ext2 file");
if (got == 0)
break;
+ if (fd != 1) {
+ nbytes = lseek64(fd, current_fs->blocksize * seek,
+ SEEK_CUR);
+ if (nbytes < 0)
+ com_err(cmdname, errno, "while lseeking file");
+ }
nbytes = write(fd, buf, got);
if ((unsigned) nbytes != got)
com_err(cmdname, errno, "while writing file");
diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
index 9148d4e..8576b1e 100644
--- a/lib/ext2fs/ext2fs.h
+++ b/lib/ext2fs/ext2fs.h
@@ -1171,6 +1171,9 @@ extern errcode_t ext2fs_file_close(ext2_file_t file);
extern errcode_t ext2fs_file_flush(ext2_file_t file);
extern errcode_t ext2fs_file_read(ext2_file_t file, void *buf,
unsigned int wanted, unsigned int *got);
+extern errcode_t ext2fs_file_read2(ext2_file_t file, void *buf,
+ unsigned int wanted, unsigned int *got,
+ ext2_off64_t *seek);
extern errcode_t ext2fs_file_write(ext2_file_t file, const void *buf,
unsigned int nbytes, unsigned int *written);
extern errcode_t ext2fs_file_llseek(ext2_file_t file, __u64 offset,
diff --git a/lib/ext2fs/fileio.c b/lib/ext2fs/fileio.c
index 1f7002c..d25ebb4 100644
--- a/lib/ext2fs/fileio.c
+++ b/lib/ext2fs/fileio.c
@@ -176,23 +176,26 @@ static errcode_t sync_buffer_position(ext2_file_t file)
* This function loads the file's block buffer with valid data from
* the disk as necessary.
*
- * If dontfill is true, then skip initializing the buffer since we're
+ * If flags is true, then skip initializing the buffer since we're
* going to be replacing its entire contents anyway. If set, then the
* function basically only sets file->physblock and EXT2_FILE_BUF_VALID
*/
#define DONTFILL 1
-static errcode_t load_buffer(ext2_file_t file, int dontfill)
+#define SEEK 2
+static errcode_t load_buffer(ext2_file_t file, int flags)
{
ext2_filsys fs = file->fs;
errcode_t retval;
+ int ret_flags;
+ int valid = 1;
if (!(file->flags & EXT2_FILE_BUF_VALID)) {
retval = ext2fs_bmap2(fs, file->ino, &file->inode,
- BMAP_BUFFER, 0, file->blockno, 0,
+ BMAP_BUFFER, 0, file->blockno, &ret_flags,
&file->physblock);
if (retval)
return retval;
- if (!dontfill) {
+ if (flags != DONTFILL) {
if (file->physblock) {
retval = io_channel_read_blk(fs->io,
file->physblock,
@@ -202,7 +205,11 @@ static errcode_t load_buffer(ext2_file_t file, int dontfill)
} else
memset(file->buf, 0, fs->blocksize);
}
- file->flags |= EXT2_FILE_BUF_VALID;
+ if (flags == SEEK && ((ret_flags & BMAP_RET_UNINIT) ||
+ file->physblock == 0))
+ valid = 0;
+ if (valid)
+ file->flags |= EXT2_FILE_BUF_VALID;
}
return 0;
}
@@ -227,20 +234,33 @@ errcode_t ext2fs_file_close(ext2_file_t file)
errcode_t ext2fs_file_read(ext2_file_t file, void *buf,
unsigned int wanted, unsigned int *got)
{
+ return ext2fs_file_read2(file, buf, wanted, got, 0);
+}
+
+
+errcode_t ext2fs_file_read2(ext2_file_t file, void *buf,
+ unsigned int wanted, unsigned int *got,
+ ext2_off64_t *seek)
+{
ext2_filsys fs;
errcode_t retval = 0;
unsigned int start, c, count = 0;
__u64 left;
char *ptr = (char *) buf;
+ int seek_cnt = 0;
+ int flags = 0;
EXT2_CHECK_MAGIC(file, EXT2_ET_MAGIC_EXT2_FILE);
fs = file->fs;
+ if (seek)
+ flags = SEEK;
+
while ((file->pos < EXT2_I_SIZE(&file->inode)) && (wanted > 0)) {
retval = sync_buffer_position(file);
if (retval)
goto fail;
- retval = load_buffer(file, 0);
+ retval = load_buffer(file, flags);
if (retval)
goto fail;
@@ -248,20 +268,26 @@ errcode_t ext2fs_file_read(ext2_file_t file, void *buf,
c = fs->blocksize - start;
if (c > wanted)
c = wanted;
- left = EXT2_I_SIZE(&file->inode) - file->pos ;
+ left = EXT2_I_SIZE(&file->inode) - file->pos;
if (c > left)
c = left;
- memcpy(ptr, file->buf+start, c);
file->pos += c;
- ptr += c;
- count += c;
- wanted -= c;
+ if (file->flags & EXT2_FILE_BUF_VALID) {
+ memcpy(ptr, file->buf+start, c);
+ ptr += c;
+ count += c;
+ wanted -= c;
+ } else {
+ seek_cnt++;
+ }
}
fail:
if (got)
*got = count;
+ if (seek)
+ *seek = seek_cnt;
return retval;
}
--
1.7.12.rc2.18.g61b472e
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