[RFC PATCH 0/1] Change failover behavior for DIRECT writes in ext4/block fops

Jeremy Bongio
2024-05-01T23:16:22Z

From: Jeremy Bongio <jbongio@google.com>

In kernel 6.9, for an O_DIRECT write:
xfs - Will fallback to a sync, buffered write for -ENOTBLK (for reflink CoW)
ext2/3/4 - will fallback to a sync, buffered write for short writes.
If iomap returns -ENOTBLK, write will return status of 0.
block fops - will fallback to a sync, buffered write for short writes.
zonefs - Will fallback to a sync, buffered write for -ENOTBLK.
Will return the bytes written for a short write, no fallback.

Relevant commit:
60263d5889e6d "iomap: fall back to buffered writes for invalidation failures"

In most cases, I think users would be surprised if an O_DIRECT write request
silently resulted in a buffered request.

The iomap_dio_rw() return code -ENOTBLK means page invalidation failed before
submitting the bio.

Is falling back to buffered IO for short writes or -ENOTBLK desirable in ext4
or block fops?

Jeremy Bongio (1):
Remove buffered failover for ext4 and block fops direct writes.

block/fops.c | 3 ---
fs/ext4/file.c | 27 ---------------------------
2 files changed, 30 deletions(-)

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2.44.0.769.g3c40516874-goog