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SubjectRe: [PATCH] fs: btrfs: Change return type to vm_fault_t
On Tue, Jun 05, 2018 at 09:16:35PM +0530, Souptick Joarder wrote:
> Use new return type vm_fault_t for 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.
>
> Ref-> commit 1c8f422059ae ("mm: change return type to vm_fault_t")
>
> vmf_error() is the newly introduce inline function
> in 4.17-rc6.
>
> Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
> ---
> fs/btrfs/ctree.h | 2 +-
> fs/btrfs/inode.c | 28 +++++++++++++---------------
> 2 files changed, 14 insertions(+), 16 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 0d422c9..1f52d9fd 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -3218,7 +3218,7 @@ int btrfs_merge_bio_hook(struct page *page, unsigned long offset,
> size_t size, struct bio *bio,
> unsigned long bio_flags);
> void btrfs_set_range_writeback(void *private_data, u64 start, u64 end);
> -int btrfs_page_mkwrite(struct vm_fault *vmf);
> +vm_fault_t btrfs_page_mkwrite(struct vm_fault *vmf);
> int btrfs_readpage(struct file *file, struct page *page);
> void btrfs_evict_inode(struct inode *inode);
> int btrfs_write_inode(struct inode *inode, struct writeback_control *wbc);
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 0b86cf1..20bde86 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -8873,7 +8873,7 @@ static void btrfs_invalidatepage(struct page *page, unsigned int offset,
> * beyond EOF, then the page is guaranteed safe against truncation until we
> * unlock the page.
> */
> -int btrfs_page_mkwrite(struct vm_fault *vmf)
> +vm_fault_t btrfs_page_mkwrite(struct vm_fault *vmf)
> {
> struct page *page = vmf->page;
> struct inode *inode = file_inode(vmf->vma->vm_file);
> @@ -8885,8 +8885,9 @@ int btrfs_page_mkwrite(struct vm_fault *vmf)
> char *kaddr;
> unsigned long zero_start;
> loff_t size;
> - int ret;
> + int err;

Please use ret2 for the variable name. We're leaving the err/ret naming
pattern and use 'ret' to match the function return value and ret2, ret3
for the temporary return values.

> int reserved = 0;
> + vm_fault_t ret;
> u64 reserved_space;
> u64 page_start;
> u64 page_end;
> @@ -8907,17 +8908,14 @@ int btrfs_page_mkwrite(struct vm_fault *vmf)
> * end up waiting indefinitely to get a lock on the page currently
> * being processed by btrfs_page_mkwrite() function.
> */
> - ret = btrfs_delalloc_reserve_space(inode, &data_reserved, page_start,
> + err = btrfs_delalloc_reserve_space(inode, &data_reserved, page_start,
> reserved_space);
> - if (!ret) {
> - ret = file_update_time(vmf->vma->vm_file);
> + if (!err) {
> + err = file_update_time(vmf->vma->vm_file);
> reserved = 1;
> }
> - if (ret) {
> - if (ret == -ENOMEM)
> - ret = VM_FAULT_OOM;
> - else /* -ENOSPC, -EIO, etc */
> - ret = VM_FAULT_SIGBUS;
> + if (err) {
> + ret = vmf_error(err);
> if (reserved)
> goto out;
> goto out_noreserve;
> @@ -8976,15 +8974,15 @@ int btrfs_page_mkwrite(struct vm_fault *vmf)
> EXTENT_DO_ACCOUNTING | EXTENT_DEFRAG,
> 0, 0, &cached_state);
>
> - ret = btrfs_set_extent_delalloc(inode, page_start, end, 0,
> + err = btrfs_set_extent_delalloc(inode, page_start, end, 0,
> &cached_state, 0);
> - if (ret) {
> + if (err) {
> unlock_extent_cached(io_tree, page_start, page_end,
> &cached_state);
> ret = VM_FAULT_SIGBUS;
> goto out_unlock;
> }
> - ret = 0;
> + err = 0;
>
> /* page is wholly or partially inside EOF */
> if (page_start + PAGE_SIZE > size)
> @@ -9009,11 +9007,11 @@ int btrfs_page_mkwrite(struct vm_fault *vmf)
> unlock_extent_cached(io_tree, page_start, page_end, &cached_state);
>
> out_unlock:
> - if (!ret) {
> + if (!err) {
> btrfs_delalloc_release_extents(BTRFS_I(inode), PAGE_SIZE, true);
> sb_end_pagefault(inode->i_sb);
> extent_changeset_free(data_reserved);
> - return VM_FAULT_LOCKED;
> + ret = VM_FAULT_LOCKED;

That's not a direct change as it changes the code flow and lets the
branch continue. As the error handling and cleanup code is partially
done in this branch continuing wrong AFAICS.

> }
> unlock_page(page);
> out:

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