[PATCH 04/10] xfs: factor out a xfs_file_write_zero_eof helper

Christoph Hellwig
2024-09-23T15:29:24Z

Split a helper from xfs_file_write_checks that just deal with the
post-EOF zeroing to keep the code readable.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/xfs/xfs_file.c | 140 +++++++++++++++++++++++++++-------------------
1 file changed, 82 insertions(+), 58 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 412b1d71b52b7d..3efb0da2a910d6 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -347,10 +347,77 @@ xfs_file_splice_read(
return ret;
}

+/*
+ * Take care of zeroing post-EOF blocks when they might exist.
+ *
+ * Returns 0 if successfully, a negative error for a failure, or 1 if this
+ * function dropped the iolock and reacquired it exclusively and the caller
+ * needs to restart the write sanity checks.
+ */
+static ssize_t
+xfs_file_write_zero_eof(
+ struct kiocb *iocb,
+ struct iov_iter *from,
+ unsigned int *iolock,
+ size_t count,
+ bool *drained_dio)
+{
+ struct xfs_inode *ip = XFS_I(iocb->ki_filp->f_mapping->host);
+ loff_t isize;
+
+ /*
+ * We need to serialise against EOF updates that occur in IO completions
+ * here. We want to make sure that nobody is changing the size while
+ * we do this check until we have placed an IO barrier (i.e. hold
+ * XFS_IOLOCK_EXCL) that prevents new IO from being dispatched. The
+ * spinlock effectively forms a memory barrier once we have
+ * XFS_IOLOCK_EXCL so we are guaranteed to see the latest EOF value and
+ * hence be able to correctly determine if we need to run zeroing.
+ */
+ spin_lock(&ip->i_flags_lock);
+ isize = i_size_read(VFS_I(ip));
+ if (iocb->ki_pos <= isize) {
+ spin_unlock(&ip->i_flags_lock);
+ return 0;
+ }
+ spin_unlock(&ip->i_flags_lock);
+
+ if (iocb->ki_flags & IOCB_NOWAIT)
+ return -EAGAIN;
+
+ if (!*drained_dio) {
+ /*
+ * If zeroing is needed and we are currently holding the iolock
+ * shared, we need to update it to exclusive which implies
+ * having to redo all checks before.
+ */
+ if (*iolock == XFS_IOLOCK_SHARED) {
+ xfs_iunlock(ip, *iolock);
+ *iolock = XFS_IOLOCK_EXCL;
+ xfs_ilock(ip, *iolock);
+ iov_iter_reexpand(from, count);
+ }
+
+ /*
+ * We now have an IO submission barrier in place, but AIO can do
+ * EOF updates during IO completion and hence we now need to
+ * wait for all of them to drain. Non-AIO DIO will have drained
+ * before we are given the XFS_IOLOCK_EXCL, and so for most
+ * cases this wait is a no-op.
+ */
+ inode_dio_wait(VFS_I(ip));
+ *drained_dio = true;
+ return 1;
+ }
+
+ trace_xfs_zero_eof(ip, isize, iocb->ki_pos - isize);
+ return xfs_zero_range(ip, isize, iocb->ki_pos - isize, NULL);
+}
+
/*
* Common pre-write limit and setup checks.
*
- * Called with the iolocked held either shared and exclusive according to
+ * Called with the iolock held either shared and exclusive according to
* @iolock, and returns with it held. Might upgrade the iolock to exclusive
* if called for a direct write beyond i_size.
*/
@@ -360,13 +427,10 @@ xfs_file_write_checks(
struct iov_iter *from,
unsigned int *iolock)
{
- struct file *file = iocb->ki_filp;
- struct inode *inode = file->f_mapping->host;
- struct xfs_inode *ip = XFS_I(inode);
- ssize_t error = 0;
+ struct inode *inode = iocb->ki_filp->f_mapping->host;
size_t count = iov_iter_count(from);
bool drained_dio = false;
- loff_t isize;
+ ssize_t error;

restart:
error = generic_write_checks(iocb, from);
@@ -389,7 +453,7 @@ xfs_file_write_checks(
* exclusively.
*/
if (*iolock == XFS_IOLOCK_SHARED && !IS_NOSEC(inode)) {
- xfs_iunlock(ip, *iolock);
+ xfs_iunlock(XFS_I(inode), *iolock);
*iolock = XFS_IOLOCK_EXCL;
error = xfs_ilock_iocb(iocb, *iolock);
if (error) {
@@ -400,64 +464,24 @@ xfs_file_write_checks(
}

/*
- * If the offset is beyond the size of the file, we need to zero any
+ * If the offset is beyond the size of the file, we need to zero all
* blocks that fall between the existing EOF and the start of this
- * write. If zeroing is needed and we are currently holding the iolock
- * shared, we need to update it to exclusive which implies having to
- * redo all checks before.
- *
- * We need to serialise against EOF updates that occur in IO completions
- * here. We want to make sure that nobody is changing the size while we
- * do this check until we have placed an IO barrier (i.e. hold the
- * XFS_IOLOCK_EXCL) that prevents new IO from being dispatched. The
- * spinlock effectively forms a memory barrier once we have the
- * XFS_IOLOCK_EXCL so we are guaranteed to see the latest EOF value and
- * hence be able to correctly determine if we need to run zeroing.
+ * write.
*
- * We can do an unlocked check here safely as IO completion can only
- * extend EOF. Truncate is locked out at this point, so the EOF can
- * not move backwards, only forwards. Hence we only need to take the
- * slow path and spin locks when we are at or beyond the current EOF.
+ * We can do an unlocked check for i_size here safely as I/O completion
+ * can only extend EOF. Truncate is locked out at this point, so the
+ * EOF can not move backwards, only forwards. Hence we only need to take
+ * the slow path when we are at or beyond the current EOF.
*/
- if (iocb->ki_pos <= i_size_read(inode))
- goto out;
-
- spin_lock(&ip->i_flags_lock);
- isize = i_size_read(inode);
- if (iocb->ki_pos > isize) {
- spin_unlock(&ip->i_flags_lock);
-
- if (iocb->ki_flags & IOCB_NOWAIT)
- return -EAGAIN;
-
- if (!drained_dio) {
- if (*iolock == XFS_IOLOCK_SHARED) {
- xfs_iunlock(ip, *iolock);
- *iolock = XFS_IOLOCK_EXCL;
- xfs_ilock(ip, *iolock);
- iov_iter_reexpand(from, count);
- }
- /*
- * We now have an IO submission barrier in place, but
- * AIO can do EOF updates during IO completion and hence
- * we now need to wait for all of them to drain. Non-AIO
- * DIO will have drained before we are given the
- * XFS_IOLOCK_EXCL, and so for most cases this wait is a
- * no-op.
- */
- inode_dio_wait(inode);
- drained_dio = true;
+ if (iocb->ki_pos > i_size_read(inode)) {
+ error = xfs_file_write_zero_eof(iocb, from, iolock, count,
+ &drained_dio);
+ if (error == 1)
goto restart;
- }
-
- trace_xfs_zero_eof(ip, isize, iocb->ki_pos - isize);
- error = xfs_zero_range(ip, isize, iocb->ki_pos - isize, NULL);
if (error)
return error;
- } else
- spin_unlock(&ip->i_flags_lock);
+ }

-out:
return kiocb_modified(iocb);
}

--
2.45.2