This commit introduces the famfs iomap_ops. When either dax_iomap_fault() or dax_iomap_rw() is called, we get a callback via our iomap_begin() handler. The question being asked is "please resolve (file, offset) to (daxdev, offset)". The function famfs_meta_to_dax_offset() does this. The per-file metadata is just an extent list to the backing dax dev. The order of this resolution is O(N) for N extents. Note with the current user space, files usually have only one extent. Signed-off-by: John Groves <john@xxxxxxxxxx> --- fs/famfs/famfs_file.c | 245 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 245 insertions(+) create mode 100644 fs/famfs/famfs_file.c diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c new file mode 100644 index 000000000000..fc667d5f7be8 --- /dev/null +++ b/fs/famfs/famfs_file.c @@ -0,0 +1,245 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * famfs - dax file system for shared fabric-attached memory + * + * Copyright 2023-2024 Micron Technology, Inc. + * + * This file system, originally based on ramfs the dax support from xfs, + * is intended to allow multiple host systems to mount a common file system + * view of dax files that map to shared memory. + */ + +#include <linux/module.h> +#include <linux/fs.h> +#include <linux/mm.h> +#include <linux/sched.h> +#include <linux/dax.h> +#include <linux/uio.h> +#include <linux/iomap.h> +#include <uapi/linux/famfs_ioctl.h> +#include "famfs_internal.h" + +/********************************************************************* + * iomap_operations + * + * This stuff uses the iomap (dax-related) helpers to resolve file offsets to + * offsets within a dax device. + */ + +/** + * famfs_meta_to_dax_offset() + * + * This function is called by famfs_iomap_begin() to resolve an offset in a file to + * an offset in a dax device. This is upcalled from dax from calls to both + * dax_iomap_fault() and dax_iomap_rw(). Dax finishes the job resolving a fault to + * a specific physical page (the fault case) or doing a memcpy variant (the rw case) + * + * Pages can be PTE (4k), PMD (2MiB) or (theoretically) PuD (1GiB) + * (these sizes are for X86; may vary on other cpu architectures + * + * @inode - the file where the fault occurred + * @iomap - struct iomap to be filled in to indicate where to find the right memory, relative + * to a dax device. + * @offset - the offset within the file where the fault occurred (will be page boundary) + * @len - the length of the faulted mapping (will be a page multiple) + * (will be trimmed in *iomap if it's disjoint in the extent list) + * @flags + */ +static int +famfs_meta_to_dax_offset( + struct inode *inode, + struct iomap *iomap, + loff_t offset, + loff_t len, + unsigned int flags) +{ + struct famfs_file_meta *meta = (struct famfs_file_meta *)inode->i_private; + int i; + loff_t local_offset = offset; + struct famfs_fs_info *fsi = inode->i_sb->s_fs_info; + + iomap->offset = offset; /* file offset */ + + for (i = 0; i < meta->tfs_extent_ct; i++) { + loff_t dax_ext_offset = meta->tfs_extents[i].offset; + loff_t dax_ext_len = meta->tfs_extents[i].len; + + if ((dax_ext_offset == 0) && (meta->file_type != FAMFS_SUPERBLOCK)) + pr_err("%s: zero offset on non-superblock file!!\n", __func__); + + /* local_offset is the offset minus the size of extents skipped so far; + * If local_offset < dax_ext_len, the data of interest starts in this extent + */ + if (local_offset < dax_ext_len) { + loff_t ext_len_remainder = dax_ext_len - local_offset; + + /*+ + * OK, we found the file metadata extent where this data begins + * @local_offset - The offset within the current extent + * @ext_len_remainder - Remaining length of ext after skipping local_offset + * + * iomap->addr is the offset within the dax device where that data + * starts + */ + iomap->addr = dax_ext_offset + local_offset; /* dax dev offset */ + iomap->offset = offset; /* file offset */ + iomap->length = min_t(loff_t, len, ext_len_remainder); + iomap->dax_dev = fsi->dax_devp; + iomap->type = IOMAP_MAPPED; + iomap->flags = flags; + + return 0; + } + local_offset -= dax_ext_len; /* Get ready for the next extent */ + } + + /* Set iomap to zero length in this case, and return 0 + * This just means that the r/w is past EOF + */ + iomap->addr = offset; + iomap->offset = offset; /* file offset */ + iomap->length = 0; /* this had better result in no access to dax mem */ + iomap->dax_dev = fsi->dax_devp; + iomap->type = IOMAP_MAPPED; + iomap->flags = flags; + + return 0; +} + +/** + * famfs_iomap_begin() + * + * This function is pretty simple because files are + * * never partially allocated + * * never have holes (never sparse) + * * never "allocate on write" + */ +static int +famfs_iomap_begin( + struct inode *inode, + loff_t offset, + loff_t length, + unsigned int flags, + struct iomap *iomap, + struct iomap *srcmap) +{ + struct famfs_file_meta *meta = inode->i_private; + size_t size; + int rc; + + size = i_size_read(inode); + + WARN_ON(size != meta->file_size); + + rc = famfs_meta_to_dax_offset(inode, iomap, offset, length, flags); + + return rc; +} + +/* Note: We never need a special set of write_iomap_ops because famfs never + * performs allocation on write. + */ +const struct iomap_ops famfs_iomap_ops = { + .iomap_begin = famfs_iomap_begin, +}; + +/********************************************************************* + * vm_operations + */ +static vm_fault_t +__famfs_filemap_fault( + struct vm_fault *vmf, + unsigned int pe_size, + bool write_fault) +{ + struct inode *inode = file_inode(vmf->vma->vm_file); + vm_fault_t ret; + + if (write_fault) { + sb_start_pagefault(inode->i_sb); + file_update_time(vmf->vma->vm_file); + } + + if (IS_DAX(inode)) { + pfn_t pfn; + + ret = dax_iomap_fault(vmf, pe_size, &pfn, NULL, &famfs_iomap_ops); + if (ret & VM_FAULT_NEEDDSYNC) + ret = dax_finish_sync_fault(vmf, pe_size, pfn); + } else { + /* All famfs faults will be dax... */ + pr_err("%s: oops, non-dax fault\n", __func__); + ret = VM_FAULT_SIGBUS; + } + + if (write_fault) + sb_end_pagefault(inode->i_sb); + + return ret; +} + +static inline bool +famfs_is_write_fault( + struct vm_fault *vmf) +{ + return (vmf->flags & FAULT_FLAG_WRITE) && + (vmf->vma->vm_flags & VM_SHARED); +} + +static vm_fault_t +famfs_filemap_fault( + struct vm_fault *vmf) +{ + /* DAX can shortcut the normal fault path on write faults! */ + return __famfs_filemap_fault(vmf, 0, + IS_DAX(file_inode(vmf->vma->vm_file)) && famfs_is_write_fault(vmf)); +} + +static vm_fault_t +famfs_filemap_huge_fault( + struct vm_fault *vmf, + unsigned int pe_size) +{ + if (!IS_DAX(file_inode(vmf->vma->vm_file))) { + pr_err("%s: file not marked IS_DAX!!\n", __func__); + return VM_FAULT_SIGBUS; + } + + /* DAX can shortcut the normal fault path on write faults! */ + return __famfs_filemap_fault(vmf, pe_size, famfs_is_write_fault(vmf)); +} + +static vm_fault_t +famfs_filemap_page_mkwrite( + struct vm_fault *vmf) +{ + return __famfs_filemap_fault(vmf, 0, true); +} + +static vm_fault_t +famfs_filemap_pfn_mkwrite( + struct vm_fault *vmf) +{ + return __famfs_filemap_fault(vmf, 0, true); +} + +static vm_fault_t +famfs_filemap_map_pages( + struct vm_fault *vmf, + pgoff_t start_pgoff, + pgoff_t end_pgoff) +{ + vm_fault_t ret; + + ret = filemap_map_pages(vmf, start_pgoff, end_pgoff); + return ret; +} + +const struct vm_operations_struct famfs_file_vm_ops = { + .fault = famfs_filemap_fault, + .huge_fault = famfs_filemap_huge_fault, + .map_pages = famfs_filemap_map_pages, + .page_mkwrite = famfs_filemap_page_mkwrite, + .pfn_mkwrite = famfs_filemap_pfn_mkwrite, +}; + -- 2.43.0