Hi Johannes
On 2/8/2022 1:54 PM, Johannes Berg wrote:
On Tue, 2022-02-08 at 13:40 -0800, Abhinav Kumar wrote:
I am checking what usermode sees and will get back ( I didnt see an
error do most likely it was EOF ). I didnt follow the second part.
I think probably it got -ENODEV, looking at kernfs_file_read_iter().
If the file descriptor read returns EOF, even if we consider them
separate how will it resolve this issue?
My earlier questions were related to fixing it in devcoredump to detect
and fix it there. Are you suggesting to fix in usermode instead? How?
Yeah, no, you cannot fix it in userspace.
But I just followed the rabbit hole down kernfs and all, and it looks
like indeed the read would be cut short with -ENODEV, sorry.
It doesn't look like there's good API for this, but it seems at least
from the underlying kernfs POV it should be possible to get_device() in
open and put_device() in release, so that the device sticks around while
somebody has the file open? It's entirely virtual, so this should be OK?
johannes
Are you suggesting something like below?
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 42dcf96..14203d0 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -32,6 +32,22 @@ static const struct sysfs_ops *sysfs_file_ops(struct
kernfs_node *kn)
return kobj->ktype ? kobj->ktype->sysfs_ops : NULL;
}
+static int sysfs_kf_open(struct kernfs_open_file *of)
+{
+ struct kobject *kobj = of->kn->parent->priv;
+ struct device *dev = kobj_to_dev(kobj);
+
+ get_device(dev);
+}
+
+static void sysfs_kf_release(struct kernfs_open_file *of)
+{
+ struct kobject *kobj = of->kn->parent->priv;
+ struct device *dev = kobj_to_dev(kobj);
+
+ put_device(dev);
+}
+
/*
* Reads on sysfs are handled through seq_file, which takes care of hairy
* details like buffering and seeking. The following function pipes
@@ -211,6 +227,8 @@ static const struct kernfs_ops sysfs_file_kfops_wo = {
};
static const struct kernfs_ops sysfs_file_kfops_rw = {
+ .open = sysfs_kf_open;
+ .release = sysfs_kf_release;
.seq_show = sysfs_kf_seq_show,
.write = sysfs_kf_write,
};
If so, dont you think this will be a more intrusive change just for the
sake of devcoredump? Any other way to keep the changes limited to
devcoredump?
Thanks
Abhinav
