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2018-09-22device-dax: Add missing address_space_operationsDave Jiang
With address_space_operations missing for device dax, namely the .set_page_dirty, we hit a kernel warning when running destructive ndctl unit test: make TESTS=device-dax check WARNING: CPU: 3 PID: 7380 at fs/buffer.c:581 __set_page_dirty+0xb1/0xc0 Setting address_space_operations to noop_set_page_dirty and noop_invalidatepage for device dax to prevent fallback to __set_page_dirty_buffers() and block_invalidatepage() respectively. Fixes: 2232c6382a ("device-dax: Enable page_mapping()") Acked-by: Jeff Moyer <jmoyer@redhat.com> Reported-by: Vishal Verma <vishal.l.verma@intel.com> Signed-off-by: Dave Jiang <dave.jiang@intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2018-09-04drivers/dax/device.c: convert variable to vm_fault_t typeSouptick Joarder
As part of 226ab561075f ("device-dax: Convert to vmf_insert_mixed and vm_fault_t") in 4.19-rc1, 'rc' was not converted to vm_fault_t. Now converted. Link: http://lkml.kernel.org/r/20180830153813.GA26059@jordon-HP-15-Notebook-PC Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Jiang <dave.jiang@intel.com> Cc: Ross Zwisler <zwisler@kernel.org> Cc: Vishal Verma <vishal.l.verma@intel.com> Cc: Matthew Wilcox <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-08-25Merge tag 'libnvdimm-for-4.19_dax-memory-failure' of ↵Linus Torvalds
gitolite.kernel.org:pub/scm/linux/kernel/git/nvdimm/nvdimm Pull libnvdimm memory-failure update from Dave Jiang: "As it stands, memory_failure() gets thoroughly confused by dev_pagemap backed mappings. The recovery code has specific enabling for several possible page states and needs new enabling to handle poison in dax mappings. In order to support reliable reverse mapping of user space addresses: 1/ Add new locking in the memory_failure() rmap path to prevent races that would typically be handled by the page lock. 2/ Since dev_pagemap pages are hidden from the page allocator and the "compound page" accounting machinery, add a mechanism to determine the size of the mapping that encompasses a given poisoned pfn. 3/ Given pmem errors can be repaired, change the speculatively accessed poison protection, mce_unmap_kpfn(), to be reversible and otherwise allow ongoing access from the kernel. A side effect of this enabling is that MADV_HWPOISON becomes usable for dax mappings, however the primary motivation is to allow the system to survive userspace consumption of hardware-poison via dax. Specifically the current behavior is: mce: Uncorrected hardware memory error in user-access at af34214200 {1}[Hardware Error]: It has been corrected by h/w and requires no further action mce: [Hardware Error]: Machine check events logged {1}[Hardware Error]: event severity: corrected Memory failure: 0xaf34214: reserved kernel page still referenced by 1 users [..] Memory failure: 0xaf34214: recovery action for reserved kernel page: Failed mce: Memory error not recovered <reboot> ...and with these changes: Injecting memory failure for pfn 0x20cb00 at process virtual address 0x7f763dd00000 Memory failure: 0x20cb00: Killing dax-pmd:5421 due to hardware memory corruption Memory failure: 0x20cb00: recovery action for dax page: Recovered Given all the cross dependencies I propose taking this through nvdimm.git with acks from Naoya, x86/core, x86/RAS, and of course dax folks" * tag 'libnvdimm-for-4.19_dax-memory-failure' of gitolite.kernel.org:pub/scm/linux/kernel/git/nvdimm/nvdimm: libnvdimm, pmem: Restore page attributes when clearing errors x86/memory_failure: Introduce {set, clear}_mce_nospec() x86/mm/pat: Prepare {reserve, free}_memtype() for "decoy" addresses mm, memory_failure: Teach memory_failure() about dev_pagemap pages filesystem-dax: Introduce dax_lock_mapping_entry() mm, memory_failure: Collect mapping size in collect_procs() mm, madvise_inject_error: Let memory_failure() optionally take a page reference mm, dev_pagemap: Do not clear ->mapping on final put mm, madvise_inject_error: Disable MADV_SOFT_OFFLINE for ZONE_DEVICE pages filesystem-dax: Set page->index device-dax: Set page->index device-dax: Enable page_mapping() device-dax: Convert to vmf_insert_mixed and vm_fault_t
2018-08-17dax: remove VM_MIXEDMAP for fsdax and device daxDave Jiang
This patch is reworked from an earlier patch that Dan has posted: https://patchwork.kernel.org/patch/10131727/ VM_MIXEDMAP is used by dax to direct mm paths like vm_normal_page() that the memory page it is dealing with is not typical memory from the linear map. The get_user_pages_fast() path, since it does not resolve the vma, is already using {pte,pmd}_devmap() as a stand-in for VM_MIXEDMAP, so we use that as a VM_MIXEDMAP replacement in some locations. In the cases where there is no pte to consult we fallback to using vma_is_dax() to detect the VM_MIXEDMAP special case. Now that we have explicit driver pfn_t-flag opt-in/opt-out for get_user_pages() support for DAX we can stop setting VM_MIXEDMAP. This also means we no longer need to worry about safely manipulating vm_flags in a future where we support dynamically changing the dax mode of a file. DAX should also now be supported with madvise_behavior(), vma_merge(), and copy_page_range(). This patch has been tested against ndctl unit test. It has also been tested against xfstests commit: 625515d using fake pmem created by memmap and no additional issues have been observed. Link: http://lkml.kernel.org/r/152847720311.55924.16999195879201817653.stgit@djiang5-desk3.ch.intel.com Signed-off-by: Dave Jiang <dave.jiang@intel.com> Acked-by: Dan Williams <dan.j.williams@intel.com> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-07-20device-dax: Set page->indexDan Williams
In support of enabling memory_failure() handling for device-dax mappings, set ->index to the pgoff of the page. The rmap implementation requires ->index to bound the search through the vma interval tree. The ->index value is never cleared. There is no possibility for the page to become associated with another pgoff while the device is enabled. When the device is disabled the 'struct page' array for the device is destroyed and ->index is reinitialized to zero. Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
2018-07-20device-dax: Enable page_mapping()Dan Williams
In support of enabling memory_failure() handling for device-dax mappings, set the ->mapping association of pages backing device-dax mappings. The rmap implementation requires page_mapping() to return the address_space hosting the vmas that map the page. The ->mapping pointer is never cleared. There is no possibility for the page to become associated with another address_space while the device is enabled. When the device is disabled the 'struct page' array for the device is destroyed / later reinitialized to zero. Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
2018-07-20device-dax: Convert to vmf_insert_mixed and vm_fault_tDan Williams
Use new return type vm_fault_t for fault and huge_fault handler. For now, this is just documenting that the function returns a VM_FAULT value rather than an errno. Once all instances are converted, vm_fault_t will become a distinct type. Commit 1c8f422059ae ("mm: change return type to vm_fault_t") Previously vm_insert_mixed() returned an error code which driver mapped into VM_FAULT_* type. The new function vmf_insert_mixed() will replace this inefficiency by returning VM_FAULT_* type. Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com> Reviewed-by: Matthew Wilcox <willy@infradead.org> Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
2018-06-28dev-dax: check_vma: ratelimit dev_info-sJeff Moyer
This is easily triggered from userspace, so let's ratelimit the messages. Signed-off-by: Jeff Moyer <jmoyer@redhat.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2018-06-06treewide: Use struct_size() for kmalloc()-familyKees Cook
One of the more common cases of allocation size calculations is finding the size of a structure that has a zero-sized array at the end, along with memory for some number of elements for that array. For example: struct foo { int stuff; void *entry[]; }; instance = kmalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL); Instead of leaving these open-coded and prone to type mistakes, we can now use the new struct_size() helper: instance = kmalloc(struct_size(instance, entry, count), GFP_KERNEL); This patch makes the changes for kmalloc()-family (and kvmalloc()-family) uses. It was done via automatic conversion with manual review for the "CHECKME" non-standard cases noted below, using the following Coccinelle script: // pkey_cache = kmalloc(sizeof *pkey_cache + tprops->pkey_tbl_len * // sizeof *pkey_cache->table, GFP_KERNEL); @@ identifier alloc =~ "kmalloc|kzalloc|kvmalloc|kvzalloc"; expression GFP; identifier VAR, ELEMENT; expression COUNT; @@ - alloc(sizeof(*VAR) + COUNT * sizeof(*VAR->ELEMENT), GFP) + alloc(struct_size(VAR, ELEMENT, COUNT), GFP) // mr = kzalloc(sizeof(*mr) + m * sizeof(mr->map[0]), GFP_KERNEL); @@ identifier alloc =~ "kmalloc|kzalloc|kvmalloc|kvzalloc"; expression GFP; identifier VAR, ELEMENT; expression COUNT; @@ - alloc(sizeof(*VAR) + COUNT * sizeof(VAR->ELEMENT[0]), GFP) + alloc(struct_size(VAR, ELEMENT, COUNT), GFP) // Same pattern, but can't trivially locate the trailing element name, // or variable name. @@ identifier alloc =~ "kmalloc|kzalloc|kvmalloc|kvzalloc"; expression GFP; expression SOMETHING, COUNT, ELEMENT; @@ - alloc(sizeof(SOMETHING) + COUNT * sizeof(ELEMENT), GFP) + alloc(CHECKME_struct_size(&SOMETHING, ELEMENT, COUNT), GFP) Signed-off-by: Kees Cook <keescook@chromium.org>
2018-04-19device-dax: allow MAP_SYNC to succeedDave Jiang
MAP_SYNC is a nop for device-dax. Allow MAP_SYNC to succeed on device-dax to eliminate special casing between device-dax and fs-dax as to when the flag can be specified. Device-dax users already implicitly assume that they do not need to call fsync(), and this enables them to explicitly check for this capability. Cc: <stable@vger.kernel.org> Fixes: b6fb293f2497 ("mm: Define MAP_SYNC and VM_SYNC flags") Signed-off-by: Dave Jiang <dave.jiang@intel.com> Reviewed-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2018-04-10Merge tag 'libnvdimm-for-4.17' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm Pull libnvdimm updates from Dan Williams: "This cycle was was not something I ever want to repeat as there were several late changes that have only now just settled. Half of the branch up to commit d2c997c0f145 ("fs, dax: use page->mapping to warn...") have been in -next for several releases. The of_pmem driver and the address range scrub rework were late arrivals, and the dax work was scaled back at the last moment. The of_pmem driver missed a previous merge window due to an oversight. A sense of obligation to rectify that miss is why it is included for 4.17. It has acks from PowerPC folks. Stephen reported a build failure that only occurs when merging it with your latest tree, for now I have fixed that up by disabling modular builds of of_pmem. A test merge with your tree has received a build success report from the 0day robot over 156 configs. An initial version of the ARS rework was submitted before the merge window. It is self contained to libnvdimm, a net code reduction, and passing all unit tests. The filesystem-dax changes are based on the wait_var_event() functionality from tip/sched/core. However, late review feedback showed that those changes regressed truncate performance to a large degree. The branch was rewound to drop the truncate behavior change and now only includes preparation patches and cleanups (with full acks and reviews). The finalization of this dax-dma-vs-trnucate work will need to wait for 4.18. Summary: - A rework of the filesytem-dax implementation provides for detection of unmap operations (truncate / hole punch) colliding with in-progress device-DMA. A fix for these collisions remains a work-in-progress pending resolution of truncate latency and starvation regressions. - The of_pmem driver expands the users of libnvdimm outside of x86 and ACPI to describe an implementation of persistent memory on PowerPC with Open Firmware / Device tree. - Address Range Scrub (ARS) handling is completely rewritten to account for the fact that ARS may run for 100s of seconds and there is no platform defined way to cancel it. ARS will now no longer block namespace initialization. - The NVDIMM Namespace Label implementation is updated to handle label areas as small as 1K, down from 128K. - Miscellaneous cleanups and updates to unit test infrastructure" * tag 'libnvdimm-for-4.17' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm: (39 commits) libnvdimm, of_pmem: workaround OF_NUMA=n build error nfit, address-range-scrub: add module option to skip initial ars nfit, address-range-scrub: rework and simplify ARS state machine nfit, address-range-scrub: determine one platform max_ars value powerpc/powernv: Create platform devs for nvdimm buses doc/devicetree: Persistent memory region bindings libnvdimm: Add device-tree based driver libnvdimm: Add of_node to region and bus descriptors libnvdimm, region: quiet region probe libnvdimm, namespace: use a safe lookup for dimm device name libnvdimm, dimm: fix dpa reservation vs uninitialized label area libnvdimm, testing: update the default smart ctrl_temperature libnvdimm, testing: Add emulation for smart injection commands nfit, address-range-scrub: introduce nfit_spa->ars_state libnvdimm: add an api to cast a 'struct nd_region' to its 'struct device' nfit, address-range-scrub: fix scrub in-progress reporting dax, dm: allow device-mapper to operate without dax support dax: introduce CONFIG_DAX_DRIVER fs, dax: use page->mapping to warn if truncate collides with a busy page ext2, dax: introduce ext2_dax_aops ...
2018-04-05device-dax: implement ->pagesize() for smaps to report MMUPageSizeDan Williams
Given that device-dax is making similar page mapping size guarantees as hugetlbfs, emit the size in smaps and any other kernel path that requests the mapping size of a vma. Link: http://lkml.kernel.org/r/151996255287.27922.18397777516059080245.stgit@dwillia2-desk3.amr.corp.intel.com Signed-off-by: Dan Williams <dan.j.williams@intel.com> Reported-by: Jane Chu <jane.chu@oracle.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Paul Mackerras <paulus@samba.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-03-06device-dax: remove redundant __func__ in dev_dbgDan Williams
Dynamic debug can be instructed to add the function name to the debug output using the +f switch, so there is no need for the dax modules to do it again. If a user decides to add the +f switch for the dax modules' dynamic debug this results in double prints of the function name. Reported-by: Johannes Thumshirn <jthumshirn@suse.de> Reported-by: Ross Zwisler <ross.zwisler@linux.intel.com> Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2018-01-23device-dax: Fix trailing semicolonLuis de Bethencourt
The trailing semicolon is an empty statement that does no operation. Removing it since it doesn't do anything. Signed-off-by: Luis de Bethencourt <luisbg@kernel.org> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2017-11-29device-dax: implement ->split() to catch invalid munmap attemptsDan Williams
Similar to how device-dax enforces that the 'address', 'offset', and 'len' parameters to mmap() be aligned to the device's fundamental alignment, the same constraints apply to munmap(). Implement ->split() to fail munmap calls that violate the alignment constraint. Otherwise, we later fail VM_BUG_ON checks in the unmap_page_range() path with crash signatures of the form: vma ffff8800b60c8a88 start 00007f88c0000000 end 00007f88c0e00000 next (null) prev (null) mm ffff8800b61150c0 prot 8000000000000027 anon_vma (null) vm_ops ffffffffa0091240 pgoff 0 file ffff8800b638ef80 private_data (null) flags: 0x380000fb(read|write|shared|mayread|maywrite|mayexec|mayshare|softdirty|mixedmap|hugepage) ------------[ cut here ]------------ kernel BUG at mm/huge_memory.c:2014! [..] RIP: 0010:__split_huge_pud+0x12a/0x180 [..] Call Trace: unmap_page_range+0x245/0xa40 ? __vma_adjust+0x301/0x990 unmap_vmas+0x4c/0xa0 unmap_region+0xae/0x120 ? __vma_rb_erase+0x11a/0x230 do_munmap+0x276/0x410 vm_munmap+0x6a/0xa0 SyS_munmap+0x1d/0x30 Link: http://lkml.kernel.org/r/151130418681.4029.7118245855057952010.stgit@dwillia2-desk3.amr.corp.intel.com Fixes: dee410792419 ("/dev/dax, core: file operations and dax-mmap") Signed-off-by: Dan Williams <dan.j.williams@intel.com> Reported-by: Jeff Moyer <jmoyer@redhat.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-10-19dev/dax: fix uninitialized variable build warningRoss Zwisler
Fix this build warning: warning: 'phys' may be used uninitialized in this function [-Wuninitialized] As reported here: https://lkml.org/lkml/2017/10/16/152 http://kisskb.ellerman.id.au/kisskb/buildresult/13181373/log/ Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2017-07-18device-dax: fix sysfs duplicate warningsDan Williams
Fix warnings of the form... WARNING: CPU: 10 PID: 4983 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x62/0x80 sysfs: cannot create duplicate filename '/class/dax/dax12.0' Call Trace: dump_stack+0x63/0x86 __warn+0xcb/0xf0 warn_slowpath_fmt+0x5a/0x80 ? kernfs_path_from_node+0x4f/0x60 sysfs_warn_dup+0x62/0x80 sysfs_do_create_link_sd.isra.2+0x97/0xb0 sysfs_create_link+0x25/0x40 device_add+0x266/0x630 devm_create_dax_dev+0x2cf/0x340 [dax] dax_pmem_probe+0x1f5/0x26e [dax_pmem] nvdimm_bus_probe+0x71/0x120 ...by reusing the namespace id for the device-dax instance name. Now that we have decided that there will never by more than one device-dax instance per libnvdimm-namespace parent device [1], we can directly reuse the namepace ids. There are some possible follow-on cleanups, but those are saved for a later patch to simplify the -stable backport. [1]: https://lists.01.org/pipermail/linux-nvdimm/2016-December/008266.html Fixes: 98a29c39dc68 ("libnvdimm, namespace: allow creation of multiple pmem...") Cc: Jeff Moyer <jmoyer@redhat.com> Cc: <stable@vger.kernel.org> Reported-by: Dariusz Dokupil <dariusz.dokupil@intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2017-07-17device-dax: fix 'passing zero to ERR_PTR()' warningDan Williams
Dan Carpenter reports: The patch 7b6be8444e0f: "dax: refactor dax-fs into a generic provider of 'struct dax_device' instances" from Apr 11, 2017, leads to the following static checker warning: drivers/dax/device.c:643 devm_create_dev_dax() warn: passing zero to 'ERR_PTR' Fix the case where we inadvertently leak 0 to ERR_PTR() by setting at every error case, and make it clear that 'count' is never 0. Reported-by: Dan Carpenter <dan.carpenter@oracle.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2017-07-06fs: new infrastructure for writeback error handling and reportingJeff Layton
Most filesystems currently use mapping_set_error and filemap_check_errors for setting and reporting/clearing writeback errors at the mapping level. filemap_check_errors is indirectly called from most of the filemap_fdatawait_* functions and from filemap_write_and_wait*. These functions are called from all sorts of contexts to wait on writeback to finish -- e.g. mostly in fsync, but also in truncate calls, getattr, etc. The non-fsync callers are problematic. We should be reporting writeback errors during fsync, but many places spread over the tree clear out errors before they can be properly reported, or report errors at nonsensical times. If I get -EIO on a stat() call, there is no reason for me to assume that it is because some previous writeback failed. The fact that it also clears out the error such that a subsequent fsync returns 0 is a bug, and a nasty one since that's potentially silent data corruption. This patch adds a small bit of new infrastructure for setting and reporting errors during address_space writeback. While the above was my original impetus for adding this, I think it's also the case that current fsync semantics are just problematic for userland. Most applications that call fsync do so to ensure that the data they wrote has hit the backing store. In the case where there are multiple writers to the file at the same time, this is really hard to determine. The first one to call fsync will see any stored error, and the rest get back 0. The processes with open fds may not be associated with one another in any way. They could even be in different containers, so ensuring coordination between all fsync callers is not really an option. One way to remedy this would be to track what file descriptor was used to dirty the file, but that's rather cumbersome and would likely be slow. However, there is a simpler way to improve the semantics here without incurring too much overhead. This set adds an errseq_t to struct address_space, and a corresponding one is added to struct file. Writeback errors are recorded in the mapping's errseq_t, and the one in struct file is used as the "since" value. This changes the semantics of the Linux fsync implementation such that applications can now use it to determine whether there were any writeback errors since fsync(fd) was last called (or since the file was opened in the case of fsync having never been called). Note that those writeback errors may have occurred when writing data that was dirtied via an entirely different fd, but that's the case now with the current mapping_set_error/filemap_check_error infrastructure. This will at least prevent you from getting a false report of success. The new behavior is still consistent with the POSIX spec, and is more reliable for application developers. This patch just adds some basic infrastructure for doing this, and ensures that the f_wb_err "cursor" is properly set when a file is opened. Later patches will change the existing code to use this new infrastructure for reporting errors at fsync time. Signed-off-by: Jeff Layton <jlayton@redhat.com> Reviewed-by: Jan Kara <jack@suse.cz>
2017-05-04Merge branch 'for-4.12/dax' into libnvdimm-for-nextDan Williams
2017-04-19dax: introduce dax_operationsDan Williams
Track a set of dax_operations per dax_device that can be set at alloc_dax() time. These operations will be used to stop the abuse of block_device_operations for communicating dax capabilities to filesystems. It will also be used to replace the "pmem api" and move pmem-specific cache maintenance, and other dax-driver-specific filesystem-dax operations, to dax device methods. In particular this allows us to stop abusing __copy_user_nocache(), via memcpy_to_pmem(), with a driver specific replacement. This is a standalone introduction of the operations. Follow on patches convert each dax-driver and teach fs/dax.c to use ->direct_access() from dax_operations instead of block_device_operations. Suggested-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2017-04-19dax: add a facility to lookup a dax device by 'host' device nameDan Williams
For the current block_device based filesystem-dax path, we need a way for it to lookup the dax_device associated with a block_device. Add a 'host' property of a dax_device that can be used for this purpose. It is a free form string, but for a dax_device associated with a block device it is the bdev name. This is a stop-gap until filesystems are able to mount on a dax-inode directly. Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2017-04-12dax: refactor dax-fs into a generic provider of 'struct dax_device' instancesDan Williams
We want dax capable drivers to be able to publish a set of dax operations [1]. However, we do not want to further abuse block_devices to advertise these operations. Instead we will attach these operations to a dax device and add a lookup mechanism to go from block device path to a dax device. A dax capable driver like pmem or brd is responsible for registering a dax device, alongside a block device, and then a dax capable filesystem is responsible for retrieving the dax device by path name if it wants to call dax_operations. For now, we refactor the dax pseudo-fs to be a generic facility, rather than an implementation detail, of the device-dax use case. Where a "dax device" is just an inode + dax infrastructure, and "Device DAX" is a mapping service layered on top of that base 'struct dax_device'. "Filesystem DAX" is then a mapping service that layers a filesystem on top of that same base device. Filesystem DAX is associated with a block_device for now, but perhaps directly to a dax device in the future, or for new pmem-only filesystems. [1]: https://lkml.org/lkml/2017/1/19/880 Suggested-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Dan Williams <dan.j.williams@intel.com>