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From: John Garry <john.g.garry@oracle.com>
To: axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me,
        jejb@linux.ibm.com, martin.petersen@oracle.com, djwong@kernel.org,
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Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
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        bvanassche@acm.org, Prasad Singamsetty <prasad.singamsetty@oracle.com>,
        John Garry <john.g.garry@oracle.com>
Subject: [PATCH v3 03/15] fs/bdev: Add atomic write support info to statx
Date: Wed, 24 Jan 2024 11:38:29 +0000
Message-Id: <20240124113841.31824-4-john.g.garry@oracle.com>
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From: Prasad Singamsetty <prasad.singamsetty@oracle.com>

Extend statx system call to return additional info for atomic write support
support if the specified file is a block device.

Signed-off-by: Prasad Singamsetty <prasad.singamsetty@oracle.com>
Signed-off-by: John Garry <john.g.garry@oracle.com>
---
 block/bdev.c              | 37 +++++++++++++++++++++---------
 fs/stat.c                 | 47 +++++++++++++++++++++++++++++++++------
 include/linux/blkdev.h    |  5 +++--
 include/linux/fs.h        |  3 +++
 include/linux/stat.h      |  3 +++
 include/uapi/linux/stat.h |  9 +++++++-
 6 files changed, 84 insertions(+), 20 deletions(-)

diff --git a/block/bdev.c b/block/bdev.c
index e9f1b12bd75c..2185084ffc89 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -1116,24 +1116,41 @@ void sync_bdevs(bool wait)
 	iput(old_inode);
 }
 
+#define BDEV_STATX_SUPPORTED_MASK (STATX_DIOALIGN | STATX_WRITE_ATOMIC)
+
 /*
- * Handle STATX_DIOALIGN for block devices.
- *
- * Note that the inode passed to this is the inode of a block device node file,
- * not the block device's internal inode.  Therefore it is *not* valid to use
- * I_BDEV() here; the block device has to be looked up by i_rdev instead.
+ * Handle STATX_{DIOALIGN, WRITE_ATOMIC} for block devices.
  */
-void bdev_statx_dioalign(struct inode *inode, struct kstat *stat)
+void bdev_statx(struct dentry *dentry, struct kstat *stat, u32 request_mask)
 {
 	struct block_device *bdev;
 
-	bdev = blkdev_get_no_open(inode->i_rdev);
+	if (!(request_mask & BDEV_STATX_SUPPORTED_MASK))
+		return;
+
+	/*
+	 * Note that d_backing_inode() returns the inode of a block device node
+	 * file, not the block device's internal inode.  Therefore it is *not*
+	 * valid to use I_BDEV() here; the block device has to be looked up by
+	 * i_rdev instead.
+	 */
+	bdev = blkdev_get_no_open(d_backing_inode(dentry)->i_rdev);
 	if (!bdev)
 		return;
 
-	stat->dio_mem_align = bdev_dma_alignment(bdev) + 1;
-	stat->dio_offset_align = bdev_logical_block_size(bdev);
-	stat->result_mask |= STATX_DIOALIGN;
+	if (request_mask & STATX_DIOALIGN) {
+		stat->dio_mem_align = bdev_dma_alignment(bdev) + 1;
+		stat->dio_offset_align = bdev_logical_block_size(bdev);
+		stat->result_mask |= STATX_DIOALIGN;
+	}
+
+	if (request_mask & STATX_WRITE_ATOMIC) {
+		struct request_queue *bd_queue = bdev->bd_queue;
+
+		generic_fill_statx_atomic_writes(stat,
+			queue_atomic_write_unit_min_bytes(bd_queue),
+			queue_atomic_write_unit_max_bytes(bd_queue));
+	}
 
 	blkdev_put_no_open(bdev);
 }
diff --git a/fs/stat.c b/fs/stat.c
index 77cdc69eb422..bd0618477702 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -89,6 +89,37 @@ void generic_fill_statx_attr(struct inode *inode, struct kstat *stat)
 }
 EXPORT_SYMBOL(generic_fill_statx_attr);
 
+/**
+ * generic_fill_statx_atomic_writes - Fill in the atomic writes statx attributes
+ * @stat:	Where to fill in the attribute flags
+ * @unit_min:	Minimum supported atomic write length
+ * @unit_max:	Maximum supported atomic write length
+ *
+ * Fill in the STATX{_ATTR}_WRITE_ATOMIC flags in the kstat structure from
+ * atomic write unit_min and unit_max values.
+ */
+void generic_fill_statx_atomic_writes(struct kstat *stat,
+				      unsigned int unit_min,
+				      unsigned int unit_max)
+{
+	/* Confirm that the request type is known */
+	stat->result_mask |= STATX_WRITE_ATOMIC;
+
+	/* Confirm that the file attribute type is known */
+	stat->attributes_mask |= STATX_ATTR_WRITE_ATOMIC;
+
+	if (unit_min) {
+		stat->atomic_write_unit_min = unit_min;
+		stat->atomic_write_unit_max = unit_max;
+		/* Initially only allow 1x segment */
+		stat->atomic_write_segments_max = 1;
+
+		/* Confirm atomic writes are actually supported */
+		stat->attributes |= STATX_ATTR_WRITE_ATOMIC;
+	}
+}
+EXPORT_SYMBOL(generic_fill_statx_atomic_writes);
+
 /**
  * vfs_getattr_nosec - getattr without security checks
  * @path: file to get attributes from
@@ -259,13 +290,12 @@ static int vfs_statx(int dfd, struct filename *filename, int flags,
 		stat->attributes |= STATX_ATTR_MOUNT_ROOT;
 	stat->attributes_mask |= STATX_ATTR_MOUNT_ROOT;
 
-	/* Handle STATX_DIOALIGN for block devices. */
-	if (request_mask & STATX_DIOALIGN) {
-		struct inode *inode = d_backing_inode(path.dentry);
-
-		if (S_ISBLK(inode->i_mode))
-			bdev_statx_dioalign(inode, stat);
-	}
+	/* If this is a block device inode, override the filesystem
+	 * attributes with the block device specific parameters
+	 * that need to be obtained from the bdev backing inode
+	 */
+	if (S_ISBLK(d_backing_inode(path.dentry)->i_mode))
+		bdev_statx(path.dentry, stat, request_mask);
 
 	path_put(&path);
 	if (retry_estale(error, lookup_flags)) {
@@ -658,6 +688,9 @@ cp_statx(const struct kstat *stat, struct statx __user *buffer)
 	tmp.stx_mnt_id = stat->mnt_id;
 	tmp.stx_dio_mem_align = stat->dio_mem_align;
 	tmp.stx_dio_offset_align = stat->dio_offset_align;
+	tmp.stx_atomic_write_unit_min = stat->atomic_write_unit_min;
+	tmp.stx_atomic_write_unit_max = stat->atomic_write_unit_max;
+	tmp.stx_atomic_write_segments_max = stat->atomic_write_segments_max;
 
 	return copy_to_user(buffer, &tmp, sizeof(tmp)) ? -EFAULT : 0;
 }
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index d5490b988918..443f08239308 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1541,7 +1541,7 @@ int sync_blockdev(struct block_device *bdev);
 int sync_blockdev_range(struct block_device *bdev, loff_t lstart, loff_t lend);
 int sync_blockdev_nowait(struct block_device *bdev);
 void sync_bdevs(bool wait);
-void bdev_statx_dioalign(struct inode *inode, struct kstat *stat);
+void bdev_statx(struct dentry *dentry, struct kstat *stat, u32 request_mask);
 void printk_all_partitions(void);
 int __init early_lookup_bdev(const char *pathname, dev_t *dev);
 #else
@@ -1559,7 +1559,8 @@ static inline int sync_blockdev_nowait(struct block_device *bdev)
 static inline void sync_bdevs(bool wait)
 {
 }
-static inline void bdev_statx_dioalign(struct inode *inode, struct kstat *stat)
+static inline void bdev_statx(struct dentry *dentry, struct kstat *stat,
+				u32 request_mask)
 {
 }
 static inline void printk_all_partitions(void)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ed5966a70495..c316c0a92fff 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3164,6 +3164,9 @@ extern const struct inode_operations page_symlink_inode_operations;
 extern void kfree_link(void *);
 void generic_fillattr(struct mnt_idmap *, u32, struct inode *, struct kstat *);
 void generic_fill_statx_attr(struct inode *inode, struct kstat *stat);
+void generic_fill_statx_atomic_writes(struct kstat *stat,
+				      unsigned int unit_min,
+				      unsigned int unit_max);
 extern int vfs_getattr_nosec(const struct path *, struct kstat *, u32, unsigned int);
 extern int vfs_getattr(const struct path *, struct kstat *, u32, unsigned int);
 void __inode_add_bytes(struct inode *inode, loff_t bytes);
diff --git a/include/linux/stat.h b/include/linux/stat.h
index 52150570d37a..2c5e2b8c6559 100644
--- a/include/linux/stat.h
+++ b/include/linux/stat.h
@@ -53,6 +53,9 @@ struct kstat {
 	u32		dio_mem_align;
 	u32		dio_offset_align;
 	u64		change_cookie;
+	u32		atomic_write_unit_min;
+	u32		atomic_write_unit_max;
+	u32		atomic_write_segments_max;
 };
 
 /* These definitions are internal to the kernel for now. Mainly used by nfsd. */
diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
index 2f2ee82d5517..c0e8e10d1de6 100644
--- a/include/uapi/linux/stat.h
+++ b/include/uapi/linux/stat.h
@@ -127,7 +127,12 @@ struct statx {
 	__u32	stx_dio_mem_align;	/* Memory buffer alignment for direct I/O */
 	__u32	stx_dio_offset_align;	/* File offset alignment for direct I/O */
 	/* 0xa0 */
-	__u64	__spare3[12];	/* Spare space for future expansion */
+	__u32	stx_atomic_write_unit_min;
+	__u32	stx_atomic_write_unit_max;
+	__u32   stx_atomic_write_segments_max;
+	__u32   __spare1;
+	/* 0xb0 */
+	__u64	__spare3[10];	/* Spare space for future expansion */
 	/* 0x100 */
 };
 
@@ -155,6 +160,7 @@ struct statx {
 #define STATX_MNT_ID		0x00001000U	/* Got stx_mnt_id */
 #define STATX_DIOALIGN		0x00002000U	/* Want/got direct I/O alignment info */
 #define STATX_MNT_ID_UNIQUE	0x00004000U	/* Want/got extended stx_mount_id */
+#define STATX_WRITE_ATOMIC	0x00008000U	/* Want/got atomic_write_* fields */
 
 #define STATX__RESERVED		0x80000000U	/* Reserved for future struct statx expansion */
 
@@ -190,6 +196,7 @@ struct statx {
 #define STATX_ATTR_MOUNT_ROOT		0x00002000 /* Root of a mount */
 #define STATX_ATTR_VERITY		0x00100000 /* [I] Verity protected file */
 #define STATX_ATTR_DAX			0x00200000 /* File is currently in DAX state */
+#define STATX_ATTR_WRITE_ATOMIC		0x00400000 /* File supports atomic write operations */
 
 
 #endif /* _UAPI_LINUX_STAT_H */
-- 
2.31.1