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e2fsprogs/debugfs/write: Input/output error when file size is zero

PATCH Applied Robert Yang 3 participants 5 messages Jul 24, 2013 – Jul 29, 2013

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Robert Yang

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#0 lore raw

Hello experts,

I met a "Input/output error" problem when used debugfs' command "write" to copy a zero size file to ext4 fs, here are the steps to reproduce the problem:

$ dd if=/dev/zero of=test.img count=1M bs=1k
$ mkfs.ext4 -F test.img
$ touch emptyfile
$ debugfs -R "write emptyfile emptyfile" -w test.img
$ mkdir mnt
$ mount test.img mnt/
$ ls mnt/emptyfile
ls: cannot access mnt/emptyfile: Input/output error

The degbufs is from the up-to-date git repo, the ext2 and ext3 work well, I think that it is caused by the EXT4_EXTENTS_FL, it works well if we turn off the EXT4_EXTENTS_FL when the file size is zero, but this is not a correct fix, would you please give me some instructions so that I can fix it?

Signature · 3 lines
Thanks

Robert
#1 lore raw
Quoted 16 lines · Robert Yang

Hello experts,

I met a "Input/output error" problem when used debugfs' command "write" to copy a zero size file to ext4 fs, here are the steps to reproduce the problem:

$ dd if=/dev/zero of=test.img count=1M bs=1k
$ mkfs.ext4 -F test.img
$ touch emptyfile
$ debugfs -R "write emptyfile emptyfile" -w test.img
$ mkdir mnt
$ mount test.img mnt/
$ ls mnt/emptyfile
ls: cannot access mnt/emptyfile: Input/output error
Quoted 5 lines

The degbufs is from the up-to-date git repo, the ext2 and ext3 work well, I think that it is caused by the EXT4_EXTENTS_FL, it works well if we turn off the EXT4_EXTENTS_FL when the file size is zero, but this is not a correct fix, would you please give me some instructions so that I can fix it?

When reporting problems like this it's helpful to include which kernel version you tested, all the error messages (including dmesg), etc.

But on upstream it persists, and when we do the ls, we get:

[40992.729130] EXT4-fs error (device loop0): ext4_ext_check_inode:464: inode #12: comm ls: bad header/extent: invalid magic - magic 0, entries 0, max 0(0), depth 0(0)

so it seems that debugfs has created a corrupt inode in the image.

I'll send a patch.

#2 lore raw

PATCH 1/1 debugfs: properly set up extent header in do_write

In reply to Robert Yang

do_write doesn't fully set up the first extent header on a new inode, so if we write a 0-length file, and don't write any data to the new file, we end up creating something that looks corrupt to kernelspace:

EXT4-fs error (device loop0): ext4_ext_check_inode:464: inode #12: comm ls: bad header/extent: invalid magic - magic 0, entries 0, max 0(0), depth 0(0)

Do something similar to ext4_ext_tree_init() here, and fill out the first extent header upon creation to avoid this.

Reported-by Robert Yang <[email protected]>
Signed-off-by Eric Sandeen <[email protected]>

---

debugfs/debugfs.c +12 -1
index dcf16e2..2660218 100644
@@ -1677,8 +1677,19 @@ void do_write(int argc, char *argv[])
 	inode.i_links_count = 1;
 	inode.i_size = statbuf.st_size;
 	if (current_fs->super->s_feature_incompat &
-	    EXT3_FEATURE_INCOMPAT_EXTENTS)
+	    EXT3_FEATURE_INCOMPAT_EXTENTS) {
+		int i;
+		struct ext3_extent_header *eh;
+
+		eh = (struct ext3_extent_header *) &inode.i_block[0];
+		eh->eh_depth = 0;
+		eh->eh_entries = 0;
+		eh->eh_magic = EXT3_EXT_MAGIC;
+		i = (sizeof(inode.i_block) - sizeof(*eh)) /
+			sizeof(struct ext3_extent);
+		eh->eh_max = ext2fs_cpu_to_le16(i);
 		inode.i_flags |= EXT4_EXTENTS_FL;
+	}
 	if (debugfs_write_new_inode(newfile, &inode, argv[0])) {
 		close(fd);
 		return;
author Tested-by on v1 1/1
#3 lore raw

Re: [PATCH] debugfs: properly set up extent header in do_write

Hi Eric,

Thank you very much, it worked well with your patch, I've tested it on Fedora 18 x86_64, the kernel is 3.6.10-4.fc18.x86_64.

Tested-by Robert Yang <[email protected]>

// Robert

Quoted 42 lines · Eric Sandeen

do_write doesn't fully set up the first extent header on a new inode, so if we write a 0-length file, and don't write any data to the new file, we end up creating something that looks corrupt to kernelspace:

EXT4-fs error (device loop0): ext4_ext_check_inode:464: inode #12: comm ls: bad header/extent: invalid magic - magic 0, entries 0, max 0(0), depth 0(0)

Do something similar to ext4_ext_tree_init() here, and fill out the first extent header upon creation to avoid this.

Reported-by Robert Yang <[email protected]>
Signed-off-by Eric Sandeen <[email protected]>

---

debugfs/debugfs.c +12 -1
index dcf16e2..2660218 100644
@@ -1677,8 +1677,19 @@ void do_write(int argc, char *argv[])
  	inode.i_links_count = 1;
  	inode.i_size = statbuf.st_size;
  	if (current_fs->super->s_feature_incompat &
-	    EXT3_FEATURE_INCOMPAT_EXTENTS)
+	    EXT3_FEATURE_INCOMPAT_EXTENTS) {
+		int i;
+		struct ext3_extent_header *eh;
+
+		eh = (struct ext3_extent_header *) &inode.i_block[0];
+		eh->eh_depth = 0;
+		eh->eh_entries = 0;
+		eh->eh_magic = EXT3_EXT_MAGIC;
+		i = (sizeof(inode.i_block) - sizeof(*eh)) /
+			sizeof(struct ext3_extent);
+		eh->eh_max = ext2fs_cpu_to_le16(i);
  		inode.i_flags |= EXT4_EXTENTS_FL;
+	}
  	if (debugfs_write_new_inode(newfile, &inode, argv[0])) {
  		close(fd);
  		return;
Applied
#4 lore raw

Re: [PATCH] debugfs: properly set up extent header in do_write

Thanks, applied.

- Ted