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__generic_file_write_iter: keep ->ki_pos and return value consistent

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A side effect worth noting: in O_APPEND case we set ->ki_pos early,
so if it turns out to be an error or a zero-length write, we'll
end up with ->ki_pos modified.  Safe, since all callers never
look at the ->ki_pos after the call of __generic_file_write_iter()
returning non-positive, all the way to caller of ->write_iter() and
those discard ->ki_pos when getting that.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2015-04-07 10:22:53 -04:00
parent e9d1593d4e
commit 0b8def9d6d
1 changed files with 10 additions and 14 deletions
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24
mm/filemap.c
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@ -2557,7 +2557,6 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
struct file *file = iocb->ki_filp;
struct address_space * mapping = file->f_mapping;
struct inode *inode = mapping->host;
loff_t pos = iocb->ki_pos;
ssize_t written = 0;
ssize_t err;
ssize_t status;
@ -2565,7 +2564,7 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
/* We can write back this queue in page reclaim */
current->backing_dev_info = inode_to_bdi(inode);
err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
err = generic_write_checks(file, &iocb->ki_pos, &count, S_ISBLK(inode->i_mode));
if (err)
goto out;
@ -2583,9 +2582,9 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
goto out;
if (io_is_direct(file)) {
loff_t endbyte;
loff_t pos, endbyte;
written = generic_file_direct_write(iocb, from, pos);
written = generic_file_direct_write(iocb, from, iocb->ki_pos);
/*
* If the write stopped short of completing, fall back to
* buffered writes. Some filesystems do this for writes to
@ -2593,13 +2592,10 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
* not succeed (even if it did, DAX does not handle dirty
* page-cache pages correctly).
*/
if (written < 0 || written == count || IS_DAX(inode))
if (written < 0 || !iov_iter_count(from) || IS_DAX(inode))
goto out;
pos += written;
count -= written;
status = generic_perform_write(file, from, pos);
status = generic_perform_write(file, from, pos = iocb->ki_pos);
/*
* If generic_perform_write() returned a synchronous error
* then we want to return the number of bytes which were
@ -2611,15 +2607,15 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
err = status;
goto out;
}
iocb->ki_pos = pos + status;
/*
* We need to ensure that the page cache pages are written to
* disk and invalidated to preserve the expected O_DIRECT
* semantics.
*/
endbyte = pos + status - 1;
err = filemap_write_and_wait_range(file->f_mapping, pos, endbyte);
err = filemap_write_and_wait_range(mapping, pos, endbyte);
if (err == 0) {
iocb->ki_pos = endbyte + 1;
written += status;
invalidate_mapping_pages(mapping,
pos >> PAGE_CACHE_SHIFT,
@ -2631,9 +2627,9 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
*/
}
} else {
written = generic_perform_write(file, from, pos);
if (likely(written >= 0))
iocb->ki_pos = pos + written;
written = generic_perform_write(file, from, iocb->ki_pos);
if (likely(written > 0))
iocb->ki_pos += written;
}
out:
current->backing_dev_info = NULL;