linux-ext4 - Re: [v13 3/5] ext4: adds project quota support

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Date:	Thu, 23 Apr 2015 02:52:21 +0800
From:	Li Xi <pkuelelixi@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Andreas Dilger <adilger@...ger.ca>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	"Theodore Ts'o" <tytso@....edu>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"hch@...radead.org" <hch@...radead.org>,
	Dmitry Monakhov <dmonakhov@...nvz.org>
Subject: Re: [v13 3/5] ext4: adds project quota support

I agree that we need to deciede which inode numbers to use for special
system file. Anyway, I will use the first way in the next version of
patch.

On Tue, Apr 21, 2015 at 8:35 PM, Jan Kara <jack@...e.cz> wrote:
> On Mon 20-04-15 17:27:20, Andreas Dilger wrote:
>> On Apr 19, 2015, at 7:39 PM, Li Xi <pkuelelixi@...il.com> 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@...e.cz>
> SUSE Labs, CR
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