On Fri, Sep 09, 2016 at 06:34:40PM +0200, Christoph Hellwig wrote:
> Very similar to the existing dax_fault function, but instead of using
> the get_block callback we rely on the iomap_ops vector from iomap.c.
> That also avoids having to do two calls into the file system for write
> faults.
>
> Signed-off-by: Christoph Hellwig <[email protected]>
> ---
> fs/dax.c | 113
> ++++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/iomap.h | 2 +
> 2 files changed, 115 insertions(+)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 57ad456..a170a94 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1343,4 +1343,117 @@ iomap_dax_rw(struct kiocb *iocb, struct iov_iter
> *iter,
> return done;
> }
> EXPORT_SYMBOL_GPL(iomap_dax_rw);
> +
> +/**
> + * iomap_dax_fault - handle a page fault on a DAX file
> + * @vma: The virtual memory area where the fault occurred
> + * @vmf: The description of the fault
> + * @ops: iomap ops passed from the file system
> + *
> + * When a page fault occurs, filesystems may call this helper in their fault
> + * or mkwrite handler for DAX files. Sssumes the caller has done all the
Assumes
> + * necessary locking for the page fault to proceed successfully.
> + */
> +int iomap_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> + struct iomap_ops *ops)
> +{
> + struct address_space *mapping = vma->vm_file->f_mapping;
> + struct inode *inode = mapping->host;
> + unsigned long vaddr = (unsigned long)vmf->virtual_address;
> + loff_t pos = (loff_t)vmf->pgoff << PAGE_SHIFT;
> + sector_t sector;
> + struct iomap iomap = { 0 };
> + unsigned flags = 0;
> + int error, major = 0;
> + void *entry;
> +
> + /*
> + * Check whether offset isn't beyond end of file now. Caller is supposed
> + * to hold locks serializing us with truncate / punch hole so this is
> + * a reliable test.
> + */
> + if (pos >= i_size_read(inode))
> + return VM_FAULT_SIGBUS;
> +
> + entry = grab_mapping_entry(mapping, vmf->pgoff);
> + if (IS_ERR(entry)) {
> + error = PTR_ERR(entry);
> + goto out;
> + }
> +
> + if ((vmf->flags & FAULT_FLAG_WRITE) && !vmf->cow_page)
> + flags |= IOMAP_WRITE;
> +
> + /*
> + * Note that we don't bother to use iomap_apply here: DAX required
> + * the file system block size to be equal the page size, which means
> + * that we never have to deal with more than a single extent here.
> + */
> + error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap);
> + if (error)
> + goto unlock_entry;
> + if (WARN_ON_ONCE(iomap.offset + iomap.length < pos + PAGE_SIZE)) {
> + error = -EIO; /* fs corruption? */
> + goto unlock_entry;
> + }
> +
> + sector = iomap.blkno + (((pos & PAGE_MASK) - iomap.offset) >> 9);
> +
> + if (vmf->cow_page) {
> + switch (iomap.type) {
> + case IOMAP_HOLE:
> + case IOMAP_UNWRITTEN:
> + clear_user_highpage(vmf->cow_page, vaddr);
> + break;
> + case IOMAP_MAPPED:
> + error = copy_user_dax(iomap.bdev, sector, PAGE_SIZE,
> + vmf->cow_page, vaddr);
> + break;
> + default:
> + WARN_ON_ONCE(1);
> + error = -EIO;
> + break;
> + }
> +
> + if (error)
> + goto unlock_entry;
> + if (!radix_tree_exceptional_entry(entry)) {
> + vmf->page = entry;
> + return VM_FAULT_LOCKED;
> + }
> + vmf->entry = entry;
> + return VM_FAULT_DAX_LOCKED;
> + }
> +
> + switch (iomap.type) {
> + case IOMAP_MAPPED:
> + if (iomap.flags & IOMAP_F_NEW) {
> + count_vm_event(PGMAJFAULT);
> + mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
> + major = VM_FAULT_MAJOR;
> + }
> + break;
> + case IOMAP_UNWRITTEN:
> + case IOMAP_HOLE:
> + if (!(vmf->flags & FAULT_FLAG_WRITE))
> + return dax_load_hole(mapping, entry, vmf);
> + default:
> + WARN_ON_ONCE(1);
> + error = -EIO;
> + }
> +
> + /* Filesystem should not return unwritten buffers to us! */
This comment is above a WARN_ON_ONCE() that checks for unwritten buffers in
dax_fault(), but that test isn't present in this code nor do we disallow
unwritten buffers (apparently, based on the IOMAP_UNWRITTEN handling above).
This comment should probably be removed.
> + error = dax_insert_mapping(mapping, iomap.bdev, sector, PAGE_SIZE,
> + &entry, vma, vmf);
> +unlock_entry:
If you stick a space in front of the labels (as is done in the rest of dax.c)
it prevents future patches from using them at the beginning of hunks. Here's a
patch adding a random space as an example:
@@ -908,6 +908,7 @@ out:
return VM_FAULT_OOM | major;
/* -EBUSY is fine, somebody else faulted on the same PTE */
if ((error < 0) && (error != -EBUSY))
return VM_FAULT_SIGBUS | major;
+
return VM_FAULT_NOPAGE | major;
}
vs
@@ -908,6 +908,7 @@ int dax_fault(struct vm_area_struct *vma, struct vm_fault
*vmf,
return VM_FAULT_OOM | major;
/* -EBUSY is fine, somebody else faulted on the same PTE */
if ((error < 0) && (error != -EBUSY))
return VM_FAULT_SIGBUS | major;
+
return VM_FAULT_NOPAGE | major;
}
where 'out' is a label without a leading space in the first case and with a
leading space in the second.
With these few nits addressed:
Reviewed-by: Ross Zwisler <[email protected]>
> + put_locked_mapping_entry(mapping, vmf->pgoff, entry);
> +out:
> + if (error == -ENOMEM)
> + return VM_FAULT_OOM | major;
> + /* -EBUSY is fine, somebody else faulted on the same PTE */
> + if (error < 0 && error != -EBUSY)
> + return VM_FAULT_SIGBUS | major;
> + return VM_FAULT_NOPAGE | major;
> +}
> +EXPORT_SYMBOL_GPL(iomap_dax_fault);
> #endif /* CONFIG_FS_IOMAP */
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 3d5f785..a4ef953 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -73,6 +73,8 @@ int iomap_truncate_page(struct inode *inode, loff_t pos,
> bool *did_zero,
> struct iomap_ops *ops);
> int iomap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
> struct iomap_ops *ops);
> +int iomap_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> + struct iomap_ops *ops);
> int iomap_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
> loff_t start, loff_t len, struct iomap_ops *ops);
>
> --
> 2.1.4
>
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> [email protected]
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