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Thu, 09 Oct 2025 15:57:38 -0700 (PDT) From: Joanne Koong To: brauner@kernel.org Cc: djwong@kernel.org, hch@infradead.org, bfoster@redhat.com, linux-fsdevel@vger.kernel.org, kernel-team@meta.com Subject: [PATCH v1 1/9] iomap: account for unaligned end offsets when truncating read range Date: Thu, 9 Oct 2025 15:56:03 -0700 Message-ID: <20251009225611.3744728-2-joannelkoong@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20251009225611.3744728-1-joannelkoong@gmail.com> References: <20251009225611.3744728-1-joannelkoong@gmail.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The end position to start truncating from may be at an offset into a block, which under the current logic would result in overtruncation. Adjust the calculation to account for unaligned end offsets. Signed-off-by: Joanne Koong --- fs/iomap/buffered-io.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index f9ae72713f74..1c6575b7e583 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -218,6 +218,22 @@ static void ifs_free(struct folio *folio) kfree(ifs); } +/* + * Calculate how many bytes to truncate based off the number of blocks to + * truncate and the end position to start truncating from. + */ +static size_t iomap_bytes_to_truncate(loff_t end_pos, unsigned block_bits, + unsigned blocks_truncated) +{ + unsigned block_size = 1 << block_bits; + unsigned block_offset = end_pos & (block_size - 1); + + if (!block_offset) + return blocks_truncated << block_bits; + + return ((blocks_truncated - 1) << block_bits) + block_offset; +} + /* * Calculate the range inside the folio that we actually need to read. */ @@ -263,7 +279,8 @@ static void iomap_adjust_read_range(struct inode *inode, struct folio *folio, /* truncate len if we find any trailing uptodate block(s) */ while (++i <= last) { if (ifs_block_is_uptodate(ifs, i)) { - plen -= (last - i + 1) * block_size; + plen -= iomap_bytes_to_truncate(*pos + plen, + block_bits, last - i + 1); last = i - 1; break; } @@ -279,7 +296,8 @@ static void iomap_adjust_read_range(struct inode *inode, struct folio *folio, unsigned end = offset_in_folio(folio, isize - 1) >> block_bits; if (first <= end && last > end) - plen -= (last - end) * block_size; + plen -= iomap_bytes_to_truncate(*pos + plen, block_bits, + last - end); } *offp = poff; -- 2.47.3