2022-04-02 13:12:00 +00:00
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.. SPDX-License-Identifier: GPL-2.0
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Large Extended Attribute Values
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-------------------------------
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To enable ext4 to store extended attribute values that do not fit in the
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inode or in the single extended attribute block attached to an inode,
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2022-09-13 18:14:27 +00:00
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the EA_INODE feature allows us to store the value in the data blocks of
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2022-04-02 13:12:00 +00:00
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a regular file inode. This “EA inode” is linked only from the extended
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attribute name index and must not appear in a directory entry. The
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2022-09-13 18:14:27 +00:00
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inode's i_atime field is used to store a checksum of the xattr value;
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and i_ctime/i_version store a 64-bit reference count, which enables
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sharing of large xattr values between multiple owning inodes. For
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backward compatibility with older versions of this feature, the
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i_mtime/i_generation *may* store a back-reference to the inode number
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and i_generation of the **one** owning inode (in cases where the EA
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inode is not referenced by multiple inodes) to verify that the EA inode
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is the correct one being accessed.
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