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. Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Valentine Sinitsyn <valesini@xxxxxxxxxxxxxx> --- Changelog: v9: - Rebased on the latest Linus tree per GregKH's request v8: - This is real v7; previous v7 is a buggy earlier patch sent by mistake v7: - Use proper locking in kernfs_fop_llseek() v6: - Mark pci_llseek_resource() as __maybe_unused - Fix a typo in pci_create_legacy_files() v5: - Fix builds without PCI mmap support (e.g. Alpha) v4: - Fix builds which #define HAVE_PCI_LEGACY (e.g. PowerPC) v3: - Grammar fixes - Add base-patch: and prerequisite-patch-id: to make kernel test robot happy v2: - Add infrastructure to customize llseek per sysfs entry type - Override llseek for PCI sysfs entries with fixed_file_llseek()-- fs/kernfs/file.c | 29 ++++++++++++++++++++++++++++- fs/sysfs/file.c | 13 +++++++++++++ include/linux/kernfs.h | 1 + include/linux/sysfs.h | 2 ++ 4 files changed, 44 insertions(+), 1 deletion(-) diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index 180906c36f51..855e3f9d8dcc 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -903,6 +903,33 @@ static __poll_t kernfs_fop_poll(struct file *filp, poll_table *wait) return ret; } +static loff_t kernfs_fop_llseek(struct file *file, loff_t offset, int whence) +{ + struct kernfs_open_file *of = kernfs_of(file); + const struct kernfs_ops *ops; + loff_t ret; + + /* + * @of->mutex nests outside active ref and is primarily to ensure that + * the ops aren't called concurrently for the same open file. + */ + mutex_lock(&of->mutex); + if (!kernfs_get_active(of->kn)) { + mutex_unlock(&of->mutex); + return -ENODEV; + } + + ops = kernfs_ops(of->kn); + if (ops->llseek) + ret = ops->llseek(of, offset, whence); + else + ret = generic_file_llseek(file, offset, whence); + + kernfs_put_active(of->kn); + mutex_unlock(&of->mutex); + return ret; +} + static void kernfs_notify_workfn(struct work_struct *work) { struct kernfs_node *kn; @@ -1005,7 +1032,7 @@ EXPORT_SYMBOL_GPL(kernfs_notify); const struct file_operations kernfs_file_fops = { .read_iter = kernfs_fop_read_iter, .write_iter = kernfs_fop_write_iter, - .llseek = generic_file_llseek, + .llseek = kernfs_fop_llseek, .mmap = kernfs_fop_mmap, .open = kernfs_fop_open, .release = kernfs_fop_release, diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c index a12ac0356c69..6b7652fb8050 100644 --- a/fs/sysfs/file.c +++ b/fs/sysfs/file.c @@ -167,6 +167,18 @@ static int sysfs_kf_bin_mmap(struct kernfs_open_file *of, return battr->mmap(of->file, kobj, battr, vma); } +static loff_t sysfs_kf_bin_llseek(struct kernfs_open_file *of, loff_t offset, + int whence) +{ + struct bin_attribute *battr = of->kn->priv; + struct kobject *kobj = of->kn->parent->priv; + + if (battr->llseek) + return battr->llseek(of->file, kobj, battr, offset, whence); + else + return generic_file_llseek(of->file, offset, whence); +} + static int sysfs_kf_bin_open(struct kernfs_open_file *of) { struct bin_attribute *battr = of->kn->priv; @@ -249,6 +261,7 @@ static const struct kernfs_ops sysfs_bin_kfops_mmap = { .write = sysfs_kf_bin_write, .mmap = sysfs_kf_bin_mmap, .open = sysfs_kf_bin_open, + .llseek = sysfs_kf_bin_llseek, }; int sysfs_add_file_mode_ns(struct kernfs_node *parent, 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); }; base-commit: 27bbf45eae9ca98877a2d52a92a188147cd61b07 -- 2.34.1