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30d61efe11
9p wants to be able to build a path from given dentry to fs root and keep it valid over a blocking operation. ->s_vfs_rename_mutex would be a natural candidate, but there are places where we need that and where we have no way to tell if ->s_vfs_rename_mutex is already held deeper in callchain. Moreover, it's only held for cross-directory renames; name changes within the same directory happen without it. Solution: * have d_move() done in ->rename() rather than in its caller * maintain a 9p-private rwsem (per-filesystem) * hold it exclusive over the relevant part of ->rename() * hold it shared over the places where we want the path. That almost works. FS_RENAME_DOES_D_MOVE is enough to put all d_move() and d_exchange() calls under filesystem's control. However, there's also __d_unalias(), which isn't covered by any of that. If ->lookup() hits a directory inode with preexisting dentry elsewhere (due to e.g. rename done on server behind our back), d_splice_alias() called by ->lookup() will move/rename that alias. Add a couple of optional methods, so that __d_unalias() would do if alias->d_op->d_unalias_trylock != NULL if (!alias->d_op->d_unalias_trylock(alias)) fail (resulting in -ESTALE from lookup) __d_move(...) if alias->d_op->d_unalias_unlock != NULL alias->d_unalias_unlock(alias) where it currently does __d_move(). 9p instances do down_write_trylock() and up_write() of ->rename_mutex. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> |
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| README | ||
Linux kernel
There are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. Please read Documentation/admin-guide/README.rst first.
In order to build the documentation, use make htmldocs or
make pdfdocs. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory, several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.