Add a new must_set_pos() helper. We will use it in follow-up patches.
Temporarily mark it as unused. This is only done to keep the diff small
and reviewable.
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
---
fs/read_write.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 52 insertions(+)
diff --git a/fs/read_write.c b/fs/read_write.c
index 66ff52860496..acee26989d95 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -85,6 +85,58 @@ loff_t vfs_setpos(struct file *file, loff_t offset, loff_t maxsize)
}
EXPORT_SYMBOL(vfs_setpos);
+/**
+ * must_set_pos - check whether f_pos has to be updated
+ * @offset: offset to use
+ * @whence: type of seek operation
+ * @eof: end of file
+ *
+ * Check whether f_pos needs to be updated and update @offset according
+ * to @whence.
+ *
+ * Return: 0 if f_pos doesn't need to be updated, 1 if f_pos has to be
+ * updated, and negative error code on failure.
+ */
+static __maybe_unused int must_set_pos(struct file *file, loff_t *offset, int whence, loff_t eof)
+{
+ switch (whence) {
+ case SEEK_END:
+ *offset += eof;
+ break;
+ case SEEK_CUR:
+ /*
+ * Here we special-case the lseek(fd, 0, SEEK_CUR)
+ * position-querying operation. Avoid rewriting the "same"
+ * f_pos value back to the file because a concurrent read(),
+ * write() or lseek() might have altered it
+ */
+ if (*offset == 0) {
+ *offset = file->f_pos;
+ return 0;
+ }
+ break;
+ case SEEK_DATA:
+ /*
+ * In the generic case the entire file is data, so as long as
+ * offset isn't at the end of the file then the offset is data.
+ */
+ if ((unsigned long long)*offset >= eof)
+ return -ENXIO;
+ break;
+ case SEEK_HOLE:
+ /*
+ * There is a virtual hole at the end of the file, so as long as
+ * offset isn't i_size or larger, return i_size.
+ */
+ if ((unsigned long long)*offset >= eof)
+ return -ENXIO;
+ *offset = eof;
+ break;
+ }
+
+ return 1;
+}
+
/**
* generic_file_llseek_size - generic llseek implementation for regular files
* @file: file structure to seek on
--
2.45.2
