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dax: provide an iomap based fault handler

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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 <hch@lst.de>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
This commit is contained in:
Christoph Hellwig 2016-09-19 11:24:50 +10:00 committed by Dave Chinner
parent a254e56812
commit a7d73fe6c5
2 changed files with 116 additions and 0 deletions
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114
fs/dax.c
View File

@ -1354,4 +1354,118 @@ iomap_dax_rw(struct kiocb *iocb, struct iov_iter *iter,
return done ? done : ret;
}
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. Assumes the caller has done all the
* 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;
}
error = dax_insert_mapping(mapping, iomap.bdev, sector,
PAGE_SIZE, &entry, vma, vmf);
break;
case IOMAP_UNWRITTEN:
case IOMAP_HOLE:
if (!(vmf->flags & FAULT_FLAG_WRITE))
return dax_load_hole(mapping, entry, vmf);
/*FALLTHRU*/
default:
WARN_ON_ONCE(1);
error = -EIO;
break;
}
unlock_entry:
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 */

2
include/linux/dax.h
View File

@ -17,6 +17,8 @@ ssize_t dax_do_io(struct kiocb *, struct inode *, struct iov_iter *,
get_block_t, dio_iodone_t, int flags);
int dax_zero_page_range(struct inode *, loff_t from, unsigned len, get_block_t);
int dax_truncate_page(struct inode *, loff_t from, get_block_t);
int iomap_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
struct iomap_ops *ops);
int dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t);
int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index);
void dax_wake_mapping_entry_waiter(struct address_space *mapping,