From 0fedefd4c4e33dd24f726b13b5d7c143e2b483be Mon Sep 17 00:00:00 2001 From: Valentine Sinitsyn Date: Mon, 25 Sep 2023 11:40:12 +0300 Subject: kernfs: sysfs: support custom llseek method for sysfs entries As of now, seeking in sysfs files is handled by generic_file_llseek(). There are situations where one may want to customize seeking logic: - Many sysfs entries are fixed files while generic_file_llseek() accepts past-the-end positions. Not only being useless by itself, this also means a bug in userspace code will trigger not at lseek(), but at some later point making debugging harder. - generic_file_llseek() relies on f_mapping->host to get the file size which might not be correct for all sysfs entries. See commit 636b21b50152 ("PCI: Revoke mappings like devmem") as an example. Implement llseek method to override this behavior at sysfs attribute level. The method is optional, and if it is absent, generic_file_llseek() is called to preserve backwards compatibility. Signed-off-by: Valentine Sinitsyn Link: https://lore.kernel.org/r/20230925084013.309399-1-valesini@yandex-team.ru Signed-off-by: Greg Kroah-Hartman --- include/linux/kernfs.h | 1 + include/linux/sysfs.h | 2 ++ 2 files changed, 3 insertions(+) (limited to 'include/linux') diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h index 2a36f3218b51..99aaa050ccb7 100644 --- a/include/linux/kernfs.h +++ b/include/linux/kernfs.h @@ -316,6 +316,7 @@ struct kernfs_ops { struct poll_table_struct *pt); int (*mmap)(struct kernfs_open_file *of, struct vm_area_struct *vma); + loff_t (*llseek)(struct kernfs_open_file *of, loff_t offset, int whence); }; /* diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h index fd3fe5c8c17f..b717a70219f6 100644 --- a/include/linux/sysfs.h +++ b/include/linux/sysfs.h @@ -181,6 +181,8 @@ struct bin_attribute { char *, loff_t, size_t); ssize_t (*write)(struct file *, struct kobject *, struct bin_attribute *, char *, loff_t, size_t); + loff_t (*llseek)(struct file *, struct kobject *, struct bin_attribute *, + loff_t, int); int (*mmap)(struct file *, struct kobject *, struct bin_attribute *attr, struct vm_area_struct *vma); }; -- cgit