linux-ext4 - [PATCH 21/31] fuse: implement fadvise for iomap files

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Message-ID: <176169810808.1424854.3451236931304006986.stgit@frogsfrogsfrogs>
Date: Tue, 28 Oct 2025 17:50:25 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: djwong@...nel.org, miklos@...redi.hu
Cc: joannelkoong@...il.com, bernd@...ernd.com, neal@...pa.dev,
 linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: [PATCH 21/31] fuse: implement fadvise for iomap files

From: Darrick J. Wong <djwong@...nel.org>

If userspace asks us to perform readahead on a file, take i_rwsem so
that it can't race with hole punching or writes.

Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
---
 fs/fuse/fuse_i.h     |    3 +++
 fs/fuse/file.c       |    1 +
 fs/fuse/file_iomap.c |   20 ++++++++++++++++++++
 3 files changed, 24 insertions(+)


diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 3fdffbeabe3306..8e3e2e5591c760 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1792,6 +1792,8 @@ int fuse_iomap_flush_unmap_range(struct inode *inode, loff_t pos,
 
 int fuse_dev_ioctl_iomap_support(struct file *file,
 				 struct fuse_iomap_support __user *argp);
+
+int fuse_iomap_fadvise(struct file *file, loff_t start, loff_t end, int advice);
 #else
 # define fuse_iomap_enabled(...)		(false)
 # define fuse_has_iomap(...)			(false)
@@ -1817,6 +1819,7 @@ int fuse_dev_ioctl_iomap_support(struct file *file,
 # define fuse_iomap_fallocate(...)		(-ENOSYS)
 # define fuse_iomap_flush_unmap_range(...)	(-ENOSYS)
 # define fuse_dev_ioctl_iomap_support(...)	(-EOPNOTSUPP)
+# define fuse_iomap_fadvise			NULL
 #endif
 
 #endif /* _FS_FUSE_I_H */
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index adcd9e3bd6a4d9..8a2daee7e58e27 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -3199,6 +3199,7 @@ static const struct file_operations fuse_file_operations = {
 	.poll		= fuse_file_poll,
 	.fallocate	= fuse_file_fallocate,
 	.copy_file_range = fuse_copy_file_range,
+	.fadvise	= fuse_iomap_fadvise,
 };
 
 static const struct address_space_operations fuse_file_aops  = {
diff --git a/fs/fuse/file_iomap.c b/fs/fuse/file_iomap.c
index ff61f7880b3332..9fd2600f599d95 100644
--- a/fs/fuse/file_iomap.c
+++ b/fs/fuse/file_iomap.c
@@ -7,6 +7,7 @@
 #include <linux/fiemap.h>
 #include <linux/pagemap.h>
 #include <linux/falloc.h>
+#include <linux/fadvise.h>
 #include "fuse_i.h"
 #include "fuse_trace.h"
 #include "iomap_i.h"
@@ -1877,3 +1878,22 @@ int fuse_dev_ioctl_iomap_support(struct file *file,
 		return -EFAULT;
 	return 0;
 }
+
+int fuse_iomap_fadvise(struct file *file, loff_t start, loff_t end, int advice)
+{
+	struct inode *inode = file_inode(file);
+	bool needlock = advice == POSIX_FADV_WILLNEED &&
+			fuse_inode_has_iomap(inode);
+	int ret;
+
+	/*
+	 * Operations creating pages in page cache need protection from hole
+	 * punching and similar ops
+	 */
+	if (needlock)
+		inode_lock_shared(inode);
+	ret = generic_fadvise(file, start, end, advice);
+	if (needlock)
+		inode_unlock_shared(inode);
+	return ret;
+}