This is similar to generic_file_llseek() but allows the caller to
specify a cookie that will be updated to indicate that a seek happened.
Caller's requiring that information in their readdir implementations can
use that.
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
---
fs/read_write.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/fs.h | 2 ++
2 files changed, 46 insertions(+)
diff --git a/fs/read_write.c b/fs/read_write.c
index ad93b72cc378..47f7b4e32a53 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -179,6 +179,50 @@ generic_file_llseek_size(struct file *file, loff_t offset, int whence,
}
EXPORT_SYMBOL(generic_file_llseek_size);
+/**
+ * generic_llseek_cookie - versioned llseek implementation
+ * @file: file structure to seek on
+ * @offset: file offset to seek to
+ * @whence: type of seek
+ * @cookie: cookie to update
+ *
+ * See generic_file_llseek for a general description and locking assumptions.
+ *
+ * In contrast to generic_file_llseek, this function also resets a
+ * specified cookie to indicate a seek took place.
+ */
+loff_t generic_llseek_cookie(struct file *file, loff_t offset, int whence,
+ u64 *cookie)
+{
+ struct inode *inode = file->f_mapping->host;
+ loff_t maxsize = inode->i_sb->s_maxbytes;
+ loff_t eof = i_size_read(inode);
+ int ret;
+
+ if (WARN_ON_ONCE(!cookie))
+ return -EINVAL;
+
+ ret = must_set_pos(file, &offset, whence, eof);
+ if (ret < 0)
+ return ret;
+ if (ret == 0)
+ return offset;
+
+ if (whence == SEEK_CUR) {
+ /*
+ * f_lock protects against read/modify/write race with
+ * other SEEK_CURs. Note that parallel writes and reads
+ * behave like SEEK_SET.
+ */
+ guard(spinlock)(&file->f_lock);
+ return vfs_setpos_cookie(file, file->f_pos + offset, maxsize,
+ cookie);
+ }
+
+ return vfs_setpos_cookie(file, offset, maxsize, cookie);
+}
+EXPORT_SYMBOL(generic_llseek_cookie);
+
/**
* generic_file_llseek - generic llseek implementation for regular files
* @file: file structure to seek on
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 58c91a52cad1..3e6b3c1afb31 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3202,6 +3202,8 @@ extern loff_t vfs_setpos(struct file *file, loff_t offset, loff_t maxsize);
extern loff_t generic_file_llseek(struct file *file, loff_t offset, int whence);
extern loff_t generic_file_llseek_size(struct file *file, loff_t offset,
int whence, loff_t maxsize, loff_t eof);
+loff_t generic_llseek_cookie(struct file *file, loff_t offset, int whence,
+ u64 *cookie);
extern loff_t fixed_size_llseek(struct file *file, loff_t offset,
int whence, loff_t size);
extern loff_t no_seek_end_llseek_size(struct file *, loff_t, int, loff_t);
--
2.45.2
