path: root/fs/seq_file.c
diff options
authorTomasz Majchrzak <tomasz.majchrzak@intel.com>2016-11-29 15:18:20 +0100
committerAl Viro <viro@zeniv.linux.org.uk>2016-12-22 23:03:06 -0500
commite522751d605d99a81508e58390a8f51ee96fb662 (patch)
tree0369ee45c1983b85350a85be34de5e7304dc1d03 /fs/seq_file.c
parent22725ce4e4a00fbc37694e25dc5c8acef8ad1c28 (diff)
seq_file: reset iterator to first record for zero offset
If kernfs file is empty on a first read, successive read operations using the same file descriptor will return no data, even when data is available. Default kernfs 'seq_next' implementation advances iterator position even when next object is not there. Kernfs 'seq_start' for following requests will not return iterator as position is already on the second object. This defect doesn't allow to monitor badblocks sysfs files from MD raid. They are initially empty but if data appears at some stage, userspace is not able to read it. Signed-off-by: Tomasz Majchrzak <tomasz.majchrzak@intel.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/seq_file.c')
1 files changed, 7 insertions, 0 deletions
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 368bfb92b115..a11f271800ef 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -190,6 +190,13 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
m->version = file->f_version;
+ /*
+ * if request is to read from zero offset, reset iterator to first
+ * record as it might have been already advanced by previous requests
+ */
+ if (*ppos == 0)
+ m->index = 0;
/* Don't assume *ppos is where we left it */
if (unlikely(*ppos != m->read_pos)) {
while ((err = traverse(m, *ppos)) == -EAGAIN)

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