3.3.2. Inode Information

Each AG manages its own inodes. The third sector in the AG contains information about the AG's inodes and is known as the AGI.

The AGI uses the following structure:

typedef struct xfs_agi {
     __be32              agi_magicnum;
     __be32              agi_versionnum;
     __be32              agi_seqno
     __be32              agi_length;
     __be32              agi_count;
     __be32              agi_root;
     __be32              agi_level;
     __be32              agi_freecount;
     __be32              agi_newino;
     __be32              agi_dirino;
     __be32              agi_unlinked[64];
} xfs_agi_t;

agi_magicnum: Specifies the magic number for the AGI sector: "XAGI" (0x58414749).
agi_versionnum: Set to XFS_AGI_VERSION which is currently 1.
agi_seqno: Specifies the AG number for the sector.
agi_length: Specifies the size of the AG in filesystem blocks.
agi_count: Specifies the number of inodes allocated for the AG.
agi_root: Specifies the block number in the AG containing the root of the inode B+tree.
agi_level: Specifies the number of levels in the inode B+tree.
agi_freecount: Specifies the number of free inodes in the AG.
agi_newino: Specifies AG relative inode number most recently allocated.
agi_dirino: Deprecated and not used, it's always set to NULL (-1).
agi_unlinked[64]: Hash table of unlinked (deleted) inodes that are still being referenced. Refer to Section 4.2, “Unlinked Pointer” for more information.