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Message-ID: <20191022225648.GD13621@mit.edu>
Date: Tue, 22 Oct 2019 18:56:48 -0400
From: "Theodore Y. Ts'o" <tytso@....edu>
To: Artem Blagodarenko <artem.blagodarenko@...il.com>
Cc: linux-ext4@...r.kernel.org, adilger.kernel@...ger.ca
Subject: Re: [PATCH] ext2fs: add ext2fs_read_sb that returns superblock
On Thu, Sep 05, 2019 at 02:01:10PM +0300, Artem Blagodarenko wrote:
> tune2fs is used to make e2label duties. ext2fs_open2() reads group
> descriptors which are not used during disk label obtaining, but takes
> a lot of time on large partitions.
>
> This patch adds ext2fs_read_sb(), there only initialized superblock
> is returned This saves time dramatically.
>
> Signed-off-by: Artem Blagodarenko <c17828@...y.com>
> Cray-bug-id: LUS-5777
Sorry for the delay in getting back to you on this. I've been
thinking about this, and I've found a better to support this
functionality by reusing the pre-existing EXT2_FLAG_SUPER_ONLY flag.
Unlike the previous version of this patch which defined
EXT2_FLAG_JOURNAL_ONLY (which was always a bit strangely named), this
avoids reading *any* block group descriptors when the file system is
open. Instead, we read the block group descriptors on demand when
ext2fs_group_desc() is called.
So this speeds up "dumpe2fs -h" as well "e2label", and we don't have
to read any block group descriptors at all. Oh, and it even works
when setting a label using e2label.
What do you think?
- Ted
commit 639e310d64dd0a2c1302eba8c3f5d0def7eacbf2
Author: Theodore Ts'o <tytso@....edu>
Date: Tue Oct 22 18:42:25 2019 -0400
Teach ext2fs_open2() to honor the EXT2_FLAG_SUPER_ONLY flag
Opening the file system with EXT2_FLAG_SUPER_ONLY will leave
fs->group_desc to be NULL and modify "dumpe2fs -h" and tune2fs when it
is emulating e2label to use this flag. This speeds up "dumpe2fs -h"
and "e2label" when operating on very large file systems.
To allow other libext2fs functions to work without too many surprises,
ext2fs_group_desc() will read in the block group descriptors on
demand. This allows "dumpe2fs -h" to be able to read the journal
inode, for example.
Signed-off-by: Theodore Ts'o <tytso@....edu>
Cray-bug-id: LUS-5777
diff --git a/lib/ext2fs/blknum.c b/lib/ext2fs/blknum.c
index 9ee5c66e..fdd51df6 100644
--- a/lib/ext2fs/blknum.c
+++ b/lib/ext2fs/blknum.c
@@ -185,9 +185,45 @@ struct ext2_group_desc *ext2fs_group_desc(ext2_filsys fs,
struct opaque_ext2_group_desc *gdp,
dgrp_t group)
{
- int desc_size = EXT2_DESC_SIZE(fs->super) & ~7;
+ struct ext2_group_desc *ret_gdp;
+ errcode_t retval;
+ static char *buf = 0;
+ static int bufsize = 0;
+ blk64_t blk;
+ int desc_size = EXT2_DESC_SIZE(fs->super) & ~7;
+ int desc_per_blk = EXT2_DESC_PER_BLOCK(fs->super);
+
+ if (group > fs->group_desc_count)
+ return NULL;
+ if (gdp)
+ return (struct ext2_group_desc *)((char *)gdp +
+ group * desc_size);
+
+ /*
+ * If fs->group_desc wasn't read in when the file system was
+ * opened, then read it on demand here.
+ */
+ if (bufsize < fs->blocksize)
+ ext2fs_free_mem(&buf);
+ if (!buf) {
+ retval = ext2fs_get_mem(fs->blocksize, &buf);
+ if (retval)
+ return NULL;
+ bufsize = fs->blocksize;
+ }
- return (struct ext2_group_desc *)((char *)gdp + group * desc_size);
+ blk = ext2fs_descriptor_block_loc2(fs, fs->super->s_first_data_block,
+ group / desc_per_blk);
+ retval = io_channel_read_blk(fs->io, blk, 1, buf);
+ if (retval)
+ return NULL;
+
+ ret_gdp = (struct ext2_group_desc *)
+ (buf + ((group % desc_per_blk) * desc_size));
+#ifdef WORDS_BIGENDIAN
+ ext2fs_swap_group_desc2(fs, ret_gdp);
+#endif
+ return ret_gdp;
}
/* Do the same but as an ext4 group desc for internal use here */
diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
index 51b54a44..ec2d6cb4 100644
--- a/lib/ext2fs/openfs.c
+++ b/lib/ext2fs/openfs.c
@@ -393,6 +393,8 @@ errcode_t ext2fs_open2(const char *name, const char *io_options,
}
fs->desc_blocks = ext2fs_div_ceil(fs->group_desc_count,
EXT2_DESC_PER_BLOCK(fs->super));
+ if (flags & EXT2_FLAG_SUPER_ONLY)
+ goto skip_read_bg;
retval = ext2fs_get_array(fs->desc_blocks, fs->blocksize,
&fs->group_desc);
if (retval)
@@ -479,7 +481,7 @@ errcode_t ext2fs_open2(const char *name, const char *io_options,
if (fs->flags & EXT2_FLAG_RW)
ext2fs_mark_super_dirty(fs);
}
-
+skip_read_bg:
if (ext2fs_has_feature_mmp(fs->super) &&
!(flags & EXT2_FLAG_SKIP_MMP) &&
(flags & (EXT2_FLAG_RW | EXT2_FLAG_EXCLUSIVE))) {
diff --git a/misc/dumpe2fs.c b/misc/dumpe2fs.c
index 384ce925..18148e2a 100644
--- a/misc/dumpe2fs.c
+++ b/misc/dumpe2fs.c
@@ -666,6 +666,8 @@ int main (int argc, char ** argv)
flags |= EXT2_FLAG_FORCE;
if (image_dump)
flags |= EXT2_FLAG_IMAGE_FILE;
+ if (header_only)
+ flags |= EXT2_FLAG_SUPER_ONLY;
try_open_again:
if (use_superblock && !use_blocksize) {
for (use_blocksize = EXT2_MIN_BLOCK_SIZE;
diff --git a/misc/tune2fs.c b/misc/tune2fs.c
index 39fce4a9..77a45875 100644
--- a/misc/tune2fs.c
+++ b/misc/tune2fs.c
@@ -1698,7 +1698,7 @@ static void parse_e2label_options(int argc, char ** argv)
argv[1]);
exit(1);
}
- open_flag = EXT2_FLAG_JOURNAL_DEV_OK;
+ open_flag = EXT2_FLAG_JOURNAL_DEV_OK | EXT2_FLAG_SUPER_ONLY;
if (argc == 3) {
open_flag |= EXT2_FLAG_RW;
L_flag = 1;
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