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Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/filesystems/netfs_library.rst | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/Documentation/filesystems/netfs_library.rst b/Documentation/filesystems/netfs_library.rst index ddd799df6..a9de281db 100644 --- a/Documentation/filesystems/netfs_library.rst +++ b/Documentation/filesystems/netfs_library.rst @@ -451,6 +451,32 @@ one. The inode should be marked ``NETFS_ICTX_SINGLE_NO_UPLOAD`` if this API is to be used. The writeback function requires the buffer to be of ITER_FOLIOQ type. +Clearing Stale Post-EOF Pagecache +--------------------------------- + +When a file is extended, data left in the pagecache past the old EOF by a write +through an mmap must not be exposed as file content. Netfslib clears this on +its own write paths, and exports a helper so a filesystem can do the same from +a resize path (truncate, setattr, fallocate and the like) that holds the +inode's ``i_rwsem`` exclusively across the whole resize:: + + void netfs_clear_stale_post_isize(struct inode *inode, uoff_t from, + uoff_t to); + +This zeroes any such data within the ``[from, to)`` hole to be made, where +@from is the old EOF and @to is the new one, and the caller must have already +updated ``i_size`` to @to before calling it. Only the folio straddling @from +can hold data written past the EOF through an mmap, as pages wholly beyond the +EOF can't be faulted in, so the zeroing is limited to that folio. The folio is +zeroed rather than dropped so that a concurrent extending write can't lose +data. + +This overlaps with ``pagecache_isize_extended()`` but can't reuse it: that +helper is keyed on a sub-page block size and is a no-op when the block size is +``>= PAGE_SIZE`` (as on network filesystems), and it doesn't wait for +writeback. As both address the same problem, a change to one should probably +be reflected in the other to keep them in sync. + High-Level VM API ================== |