diff options
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/dax.txt | 22 | ||||
| -rw-r--r-- | Documentation/filesystems/ext4.txt | 13 |
2 files changed, 17 insertions, 18 deletions
diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt index 23d18b8a49d5..a7e6e14aeb08 100644 --- a/Documentation/filesystems/dax.txt +++ b/Documentation/filesystems/dax.txt @@ -58,22 +58,22 @@ Implementation Tips for Filesystem Writers Filesystem support consists of - adding support to mark inodes as being DAX by setting the S_DAX flag in i_flags -- implementing the direct_IO address space operation, and calling - dax_do_io() instead of blockdev_direct_IO() if S_DAX is set +- implementing ->read_iter and ->write_iter operations which use dax_iomap_rw() + when inode has S_DAX flag set - implementing an mmap file operation for DAX files which sets the VM_MIXEDMAP and VM_HUGEPAGE flags on the VMA, and setting the vm_ops to - include handlers for fault, pmd_fault and page_mkwrite (which should - probably call dax_fault(), dax_pmd_fault() and dax_mkwrite(), passing the - appropriate get_block() callback) -- calling dax_truncate_page() instead of block_truncate_page() for DAX files -- calling dax_zero_page_range() instead of zero_user() for DAX files + include handlers for fault, pmd_fault, page_mkwrite, pfn_mkwrite. These + handlers should probably call dax_iomap_fault() (for fault and page_mkwrite + handlers), dax_iomap_pmd_fault(), dax_pfn_mkwrite() passing the appropriate + iomap operations. +- calling iomap_zero_range() passing appropriate iomap operations instead of + block_truncate_page() for DAX files - ensuring that there is sufficient locking between reads, writes, truncates and page faults -The get_block() callback passed to the DAX functions may return -uninitialised extents. If it does, it must ensure that simultaneous -calls to get_block() (for example by a page-fault racing with a read() -or a write()) work correctly. +The iomap handlers for allocating blocks must make sure that allocated blocks +are zeroed out and converted to written extents before being returned to avoid +exposure of uninitialized data through mmap. These filesystems may be used for inspiration: - ext2: see Documentation/filesystems/ext2.txt diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt index 6c0108eb0137..3698ed3146e3 100644 --- a/Documentation/filesystems/ext4.txt +++ b/Documentation/filesystems/ext4.txt @@ -351,14 +351,13 @@ nouid32 Disables 32-bit UIDs and GIDs. This is for interoperability with older kernels which only store and expect 16-bit values. -block_validity This options allows to enables/disables the in-kernel +block_validity(*) These options enable or disable the in-kernel noblock_validity facility for tracking filesystem metadata blocks - within internal data structures. This allows multi- - block allocator and other routines to quickly locate - extents which might overlap with filesystem metadata - blocks. This option is intended for debugging - purposes and since it negatively affects the - performance, it is off by default. + within internal data structures. This allows multi- + block allocator and other routines to notice + bugs or corrupted allocation bitmaps which cause + blocks to be allocated which overlap with + filesystem metadata blocks. dioread_lock Controls whether or not ext4 should use the DIO read dioread_nolock locking. If the dioread_nolock option is specified |