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Diffstat (limited to 'Documentation/filesystems/aufs/design/10dynop.txt')
| -rw-r--r-- | Documentation/filesystems/aufs/design/10dynop.txt | 34 |
1 files changed, 0 insertions, 34 deletions
diff --git a/Documentation/filesystems/aufs/design/10dynop.txt b/Documentation/filesystems/aufs/design/10dynop.txt deleted file mode 100644 index 49afc5899..000000000 --- a/Documentation/filesystems/aufs/design/10dynop.txt +++ /dev/null @@ -1,34 +0,0 @@ - -# Copyright (C) 2010-2016 Junjiro R. Okajima - -Dynamically customizable FS operations ----------------------------------------------------------------------- -Generally FS operations (struct inode_operations, struct -address_space_operations, struct file_operations, etc.) are defined as -"static const", but it never means that FS have only one set of -operation. Some FS have multiple sets of them. For instance, ext2 has -three sets, one for XIP, for NOBH, and for normal. -Since aufs overrides and redirects these operations, sometimes aufs has -to change its behaviour according to the branch FS type. More importantly -VFS acts differently if a function (member in the struct) is set or -not. It means aufs should have several sets of operations and select one -among them according to the branch FS definition. - -In order to solve this problem and not to affect the behaviour of VFS, -aufs defines these operations dynamically. For instance, aufs defines -dummy direct_IO function for struct address_space_operations, but it may -not be set to the address_space_operations actually. When the branch FS -doesn't have it, aufs doesn't set it to its address_space_operations -while the function definition itself is still alive. So the behaviour -itself will not change, and it will return an error when direct_IO is -not set. - -The lifetime of these dynamically generated operation object is -maintained by aufs branch object. When the branch is removed from aufs, -the reference counter of the object is decremented. When it reaches -zero, the dynamically generated operation object will be freed. - -This approach is designed to support AIO (io_submit), Direct I/O and -XIP (DAX) mainly. -Currently this approach is applied to address_space_operations for -regular files only. |