On Mon 20-04-15 17:27:20, Andreas Dilger wrote:
> On Apr 19, 2015, at 7:39 PM, Li Xi <pkuelelixi@xxxxxxxxx> wrote:
...
> > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> > index 1446c4f..a7acf10 100644
> > --- a/fs/ext4/ext4.h
> > +++ b/fs/ext4/ext4.h
> > @@ -1169,7 +1169,8 @@ struct ext4_super_block {
> > __le32 s_overhead_clusters; /* overhead blocks/clusters in fs */
> > __le32 s_backup_bgs[2]; /* groups with sparse_super2 SBs */
> > __u8 s_encrypt_algos[4]; /* Encryption algorithms in use */
> > - __le32 s_reserved[105]; /* Padding to the end of the block */
> > + __le32 s_prj_quota_inum; /* inode for tracking project quota */
> > + __le32 s_reserved[104]; /* Padding to the end of the block */
> > __le32 s_checksum; /* crc32c(superblock) */
> > };
> >
> > @@ -1184,7 +1185,7 @@ struct ext4_super_block {
> > #define EXT4_MF_FS_ABORTED 0x0002 /* Fatal error detected */
> >
> > /* Number of quota types we support */
> > -#define EXT4_MAXQUOTAS 2
> > +#define EXT4_MAXQUOTAS 3
> >
> > /*
> > * fourth extended-fs super-block data in memory
> > @@ -1376,6 +1377,7 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
> > ino == EXT4_BOOT_LOADER_INO ||
> > ino == EXT4_JOURNAL_INO ||
> > ino == EXT4_RESIZE_INO ||
> > + ino == le32_to_cpu(EXT4_SB(sb)->s_es->s_prj_quota_inum) ||
>
> This extra check isn't needed, since s_proj_quota_inum will be a regular
> inode number and handled by the checks below.
So I think this needs a final decision from Ted how we handle new system
files and use it consistently among all features - project quotas, orphan
file, etc. Ted, can you share your thoughts please? Options are:
1) We allocate inodes from normal inode pool and just store their inode
numbers in superblock.
+ no need to increase number of special inodes
- slightly less robust since inode can be anywhere
- needs special treatment from fsck to know inode isn't just some lost inode
- consumes space in sb for inode numbers
2) Like 1) but also create special "system" directory and attach system
inodes there
+ fsck just needs to know about the system directory, not about every
special file
+ no wasted space in sb for every special inode
- more code in kernel to implement this
- even less robust than 1) - when system directory gets corrupt, we are in
trouble
3) Increase number of special inodes
+ consistent with what we did upto now
+ somewhat more robust since inode is in fixed place
- tune2fs needs to do quite some work to reserve more inodes
- wastes unused special inodes
Honza
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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