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The current cursor-based directory offset mechanism doesn't work when a tmpfs filesystem is exported via NFS. This is because NFS clients do not open directories. Each server-side READDIR operation has to open the directory, read it, then close it. The cursor state for that directory, being associated strictly with the opened struct file, is thus discarded after each NFS READDIR operation. Directory offsets are cached not only by NFS clients, but also by user space libraries on those clients. Essentially there is no way to invalidate those caches when directory offsets have changed on an NFS server after the offset-to-dentry mapping changes. Thus the whole application stack depends on unchanging directory offsets. The solution we've come up with is to make the directory offset for each file in a tmpfs filesystem stable for the life of the directory entry it represents. shmem_readdir() and shmem_dir_llseek() now use an xarray to map each directory offset (an loff_t integer) to the memory address of a struct dentry. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Message-Id: <168814734331.530310.3911190551060453102.stgit@manet.1015granger.net> Signed-off-by: Christian Brauner <brauner@kernel.org>
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 Restructured Text 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.