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Date: Mon, 14 Jan 2013 22:18:30 +0800
From: Zheng Liu <gnehzuil.liu@...il.com>
To: linux-ext4@...r.kernel.org
Cc: "Theodore Ts'o" <tytso@....edu>, Zheng Liu <wenqing.lz@...bao.com>
Subject: [PATCH 1/2 v2] libext2fs: introduce lseek SEEK_DATA/HOLE
From: Zheng Liu <wenqing.lz@...bao.com>
ext2fs_file_llseek is extented to introduce SEEK_DATA/HOLE. In *_data()
function it will find the next data, and in *_hole() function it will find the
next hole. A new error code called EXT2_ET_SEEK_BEYOND_EOF is define to
indicate that the offset is beyond the end of file.
Here they need to solve a problem that the caller can not dereference
ext2_file_t->pos because this structure is hidden by a typedef. Thus,
EXT2_SEEK_OFFSET_INVALID is define to indicate whether or not it will
find the data/hole from ext2_file_t->pos.
CC: "Theodore Ts'o" <tytso@....edu>
Signed-off-by: Zheng Liu <wenqing.lz@...bao.com>
---
Hi Ted,
ext2fs_file_llseek_data/hole() seem to be weird because ext2_file_t structure is
hidden by a typedef. The caller can not dereference it. So I define a marco
called EXT2_SEEK_OFFSET_INVALID to let the caller indicate that it find the
data/hole from ext2_file_t->pos or from offset. What do you think?
Thanks,
- Zheng
lib/ext2fs/ext2_err.et.in | 3 ++
lib/ext2fs/ext2fs.h | 4 +++
lib/ext2fs/fileio.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++-
3 files changed, 86 insertions(+), 1 deletion(-)
diff --git a/lib/ext2fs/ext2_err.et.in b/lib/ext2fs/ext2_err.et.in
index c99a167..f763938 100644
--- a/lib/ext2fs/ext2_err.et.in
+++ b/lib/ext2fs/ext2_err.et.in
@@ -473,4 +473,7 @@ ec EXT2_ET_UNKNOWN_CSUM,
ec EXT2_ET_MMP_CSUM_INVALID,
"MMP block checksum does not match MMP block"
+ec EXT2_ET_SEEK_BEYOND_EOF,
+ "lseek beyond the EOF"
+
end
diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
index 7139b4d..474049f 100644
--- a/lib/ext2fs/ext2fs.h
+++ b/lib/ext2fs/ext2fs.h
@@ -160,6 +160,10 @@ typedef struct ext2_file *ext2_file_t;
#define EXT2_SEEK_SET 0
#define EXT2_SEEK_CUR 1
#define EXT2_SEEK_END 2
+#define EXT2_SEEK_DATA 3
+#define EXT2_SEEK_HOLE 4
+
+#define EXT2_SEEK_OFFSET_INVALID -1
/*
* Flags for the ext2_filsys structure and for ext2fs_open()
diff --git a/lib/ext2fs/fileio.c b/lib/ext2fs/fileio.c
index 1f7002c..ab33290 100644
--- a/lib/ext2fs/fileio.c
+++ b/lib/ext2fs/fileio.c
@@ -312,10 +312,84 @@ fail:
return retval;
}
+static errcode_t ext2fs_file_llseek_data(ext2_file_t file, __u64 offset)
+{
+ int ret_flags, flag = 1;
+ ext2_filsys fs = file->fs;
+ errcode_t retval;
+
+ /*
+ * If offset == EXT2_SEEK_OFFSET_INVALID, that means that
+ * the caller wants to find the data from file->pos.
+ */
+ offset = offset != EXT2_SEEK_OFFSET_INVALID ? offset : file->pos;
+ file->blockno = offset / fs->blocksize;
+ while (file->blockno * fs->blocksize < EXT2_I_SIZE(&file->inode)) {
+ retval = ext2fs_bmap2(fs, file->ino, &file->inode,
+ BMAP_BUFFER, 0, file->blockno,
+ &ret_flags, &file->physblock);
+ if (retval)
+ return retval;
+ if (file->physblock == 0 || (ret_flags & BMAP_RET_UNINIT)) {
+ file->blockno++;
+ flag = 0;
+ } else {
+ if (flag)
+ file->pos = offset;
+ else
+ file->pos = file->blockno * fs->blocksize;
+ break;
+ }
+ }
+
+ /* notify the caller that there is no any data */
+ if (file->blockno * fs->blocksize >= EXT2_I_SIZE(&file->inode))
+ return EXT2_ET_SEEK_BEYOND_EOF;
+
+ return 0;
+}
+
+static errcode_t ext2fs_file_llseek_hole(ext2_file_t file, __u64 offset)
+{
+ int ret_flags, flag = 1;
+ ext2_filsys fs = file->fs;
+ errcode_t retval;
+
+ /*
+ * If offset == EXT2_SEEK_OFFSET_INVALID, that means that
+ * the caller wants to find the hole from file->pos.
+ */
+ offset = offset != EXT2_SEEK_OFFSET_INVALID ? offset : file->pos;
+ if (offset >= EXT2_I_SIZE(&file->inode))
+ return EXT2_ET_SEEK_BEYOND_EOF;
+
+ file->blockno = offset / fs->blocksize;
+ while (file->blockno * fs->blocksize < EXT2_I_SIZE(&file->inode)) {
+ retval = ext2fs_bmap2(fs, file->ino, &file->inode,
+ BMAP_BUFFER, 0, file->blockno,
+ &ret_flags, &file->physblock);
+ if (retval)
+ return retval;
+ if (file->physblock == 0 || (ret_flags & BMAP_RET_UNINIT)) {
+ if (flag)
+ file->pos = offset;
+ else
+ file->pos = file->blockno * fs->blocksize;
+ break;
+ } else {
+ file->blockno++;
+ flag = 0;
+ }
+ }
+
+ return 0;
+}
+
errcode_t ext2fs_file_llseek(ext2_file_t file, __u64 offset,
int whence, __u64 *ret_pos)
{
EXT2_CHECK_MAGIC(file, EXT2_ET_MAGIC_EXT2_FILE);
+ errcode_t retval = 0;
if (whence == EXT2_SEEK_SET)
file->pos = offset;
@@ -323,13 +397,17 @@ errcode_t ext2fs_file_llseek(ext2_file_t file, __u64 offset,
file->pos += offset;
else if (whence == EXT2_SEEK_END)
file->pos = EXT2_I_SIZE(&file->inode) + offset;
+ else if (whence == EXT2_SEEK_DATA)
+ retval = ext2fs_file_llseek_data(file, offset);
+ else if (whence == EXT2_SEEK_HOLE)
+ retval = ext2fs_file_llseek_hole(file, offset);
else
return EXT2_ET_INVALID_ARGUMENT;
if (ret_pos)
*ret_pos = file->pos;
- return 0;
+ return retval;
}
errcode_t ext2fs_file_lseek(ext2_file_t file, ext2_off_t offset,
--
1.7.12.rc2.18.g61b472e
--
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