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    SubjectRe: [PATCH v14 078/138] mm/filemap: Add folio_mkwrite_check_truncate()
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    On 7/15/21 5:36 AM, Matthew Wilcox (Oracle) wrote:
    > This is the folio equivalent of page_mkwrite_check_truncate().
    >
    > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    > ---
    > include/linux/pagemap.h | 28 ++++++++++++++++++++++++++++
    > 1 file changed, 28 insertions(+)
    >
    > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
    > index 412db88b8d0c..18c06c3e42c3 100644
    > --- a/include/linux/pagemap.h
    > +++ b/include/linux/pagemap.h
    > @@ -1121,6 +1121,34 @@ static inline unsigned long dir_pages(struct inode *inode)
    > PAGE_SHIFT;
    > }
    >
    > +/**
    > + * folio_mkwrite_check_truncate - check if folio was truncated
    > + * @folio: the folio to check
    > + * @inode: the inode to check the folio against
    > + *
    > + * Return: the number of bytes in the folio up to EOF,
    > + * or -EFAULT if the folio was truncated.
    > + */
    > +static inline ssize_t folio_mkwrite_check_truncate(struct folio *folio,
    > + struct inode *inode)
    > +{
    > + loff_t size = i_size_read(inode);
    > + pgoff_t index = size >> PAGE_SHIFT;
    > + size_t offset = offset_in_folio(folio, size);
    > +
    > + if (!folio->mapping)

    The check in the page_ version is
    if (page->mapping != inode->i_mapping)

    Why is the one above sufficient?

    > + return -EFAULT;
    > +
    > + /* folio is wholly inside EOF */
    > + if (folio_next_index(folio) - 1 < index)
    > + return folio_size(folio);
    > + /* folio is wholly past EOF */
    > + if (folio->index > index || !offset)
    > + return -EFAULT;
    > + /* folio is partially inside EOF */
    > + return offset;
    > +}
    > +
    > /**
    > * page_mkwrite_check_truncate - check if page was truncated
    > * @page: the page to check
    >

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