linux-kernel - [PATCH v2] loop: use vfs_getattr

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Message-ID: <20250811190303.222802-1-rajeevm@hpe.com>
Date: Mon, 11 Aug 2025 19:03:03 +0000
From: Rajeev Mishra <rajeevm@....com>
To: axboe@...nel.dk, yukuai1@...weicloud.com
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Rajeev Mishra <rajeevm@....com>
Subject: [PATCH v2] loop: use vfs_getattr_nosec() for accurate file size

The get_size() function now uses vfs_getattr_nosec() instead of
i_size_read() to obtain file size information. This provides more
accurate results for network filesystems where cached metadata
may be stale, ensuring the loop device reflects the current file
size rather than potentially outdated cached values.

Signed-off-by: Rajeev Mishra <rajeevm@....com>
---
 drivers/block/loop.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 1b6ee91f8eb9..c418c47db76e 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -137,12 +137,32 @@ static void loop_global_unlock(struct loop_device *lo, bool global)
 static int max_part;
 static int part_shift;
 
+/**
+ * get_size - calculate the effective size of a loop device
+ * @offset: offset into the backing file
+ * @sizelimit: user-specified size limit
+ * @file: the backing file
+ *
+ * Calculate the effective size of the loop device
+ *
+ * Returns: size in 512-byte sectors, or 0 if invalid
+ */
 static loff_t get_size(loff_t offset, loff_t sizelimit, struct file *file)
 {
+	struct kstat stat;
 	loff_t loopsize;
+	int ret;
+
+	/*
+	 * Get the accurate file size. This will prevent caching
+	 * issue that occurs at filesystem layer.
+	 */
+	ret = vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE, 0);
+	if (ret)
+		return 0;
+
+	loopsize = stat.size;
 
-	/* Compute loopsize in bytes */
-	loopsize = i_size_read(file->f_mapping->host);
 	if (offset > 0)
 		loopsize -= offset;
 	/* offset is beyond i_size, weird but possible */
-- 
2.43.7