btrfs-progs: new --inode-flags option #987
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Inside btrfs-progs (mostly 'mkfs/rootdir.c') new inodes are created in a different way than the kernel: - A new orphan inode item is created Without knowing the parent inode, thus it will always have the default flags (0). - Link the new inode to a parent Meanwhile inside the kernel, we know exactly the parent inode at new inode creation time, and can inherit the inode flags (NODATACOW/NODATASUM/COMPRESS/etc). Address the missing ability by: - Inherit the parent inode flags when linking an orphan inode The function btrfs_add_link() is called when linking an inode. It can be called to creating the initial link if it's a new and orphan inode. It can also be called to creating extra hard links. If the inode is already orphan, we know it's newly created and should inherit the inode flag from the parent. With this new ability, it will be much easier to implement new per-inode flags (like NODATACOW/NODATASUM) and get them properly passed down. Signed-off-by: Qu Wenruo <wqu@suse.com>
NODATACOW or NODATASUM Currently mkfs.btrfs --rootdir is implying data checksum, but soon we will support per-inode NODATACOW|NODATASUM flags. To support per-inode NODATACOW|NODATASUM flags: - Avoid compression if the inode has either NODATACOW|NODATASUM flag - Do not generate data checksum if the inode has either NODATACOW|NODATASUM flag. Both behaviors are the following the kernel ones. Signed-off-by: Qu Wenruo <wqu@suse.com>
This new option allows end users to specify certain per-inode flags for
specified file/directory inside rootdir.
And mkfs will follow the kernel behavior by inheriting the inode flag
from the parent.
For example:
rootdir
|- file1
|- file2
|- dir1/
| |- file3
|- subv/ << will be created as a subvolume using --subvol option
|- dir2/
| |- file4
|- file5
When `mkfs.btrfs --rootdir rootdir --subvol subv --inode-flags
nodatacow:dir1 --inode-flags nodatacow:subv", then the following files
and directory will have *nodatacow* flag set:
- dir1
- file3
- subv
- dir2
- file4
- file5
For now only two flags are supported:
- nodatacow
Disable data COW, implies *nodatasum* for regular files
- nodatasum
Disable data checksum only.
This also works with --compress option, and files with nodatasum or
nodatacow flag will skip compression.
Signed-off-by: Qu Wenruo <wqu@suse.com>
The simple test will create a layout like the following: rootdir |- file1 |- file2 |- subv/ << Regular subvolume | |- file3 |- nocow_subv/ << NODATACOW subvolume | |- file4 |- nocow_dir/ << NODATACOW directory | |- dir2 | | |- file5 | |- file6 |- nocow_file1 << NODATACOW file Any files under NODATACOW subvolume/directory should also be NODATACOW. The explicitly specified single file should also be NODATACOW. Signed-off-by: Qu Wenruo <wqu@suse.com>
![github-advanced-security[bot]](https://avatars.githubusercontent.com/in/57789?s=60&v=4){kind=small}
| @@ -1686,6 +1764,7 @@ | |||
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| g_trans = trans; | |||
| g_subvols = subvols; | |||
| g_inode_flags_list = inode_flags_list; | |||
Check warning
Code scanning / CodeQL
Local variable address stored in non-local memory Warning
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The new --inode-flags option allows us to specify certain btrfs specific
flags to each inode.
Currently we only support nodatacow and nodatasum.
But in the future compression flag can also be added, allowing more
accurate per-file compression.
Furthermore child inodes will inherit the flag from their parents,
meaning one only needs to specify the flag to the parent directory, then
all children files/directories will have the flag.
This new option also works well with --subvol, although one has to
note that, the inode flag inheritance does not cross subvolume boundary
(the same as the kernel).
Finally, nodatacow and nodatasum will disable compression, just like the
kernel.
I hope this will helps projects like
mkosiandyoctoto build theirimages with more btrfs specific flags.
The only downside for now is the memory usage, both
--subvoland--inode-flagswill take over 8K for each specification.So one should not specify them too many times.