Re: [PATCH v2 2/9] eventfs: adding eventfs dir add functions

[Ajay Kaher]

> On 08-May-2023, at 3:02 PM, Zheng Yejian <zhengyejian1@xxxxxxxxxx> wrote:
> 
> On 2023/5/2 19:23, Ajay Kaher wrote:
>> Adding eventfs_file structure which will hold properties of file or dir.
>> 
>> Adding following functions to add dir in eventfs:
>> 
>> eventfs_create_events_dir() will directly create events dir with-in
>> tracing folder.
>> 
>> eventfs_add_subsystem_dir() will adds the info of subsystem_dir to
>> eventfs and dynamically create subsystem_dir as and when requires.
>> 
>> eventfs_add_dir() will add the info of dir (which is with-in
>> subsystem_dir) to eventfs and dynamically create these dir as
>> and when requires.
>> 
>> Signed-off-by: Ajay Kaher <akaher@xxxxxxxxxx>
>> Co-developed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
>> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
>> Tested-by: Ching-lin Yu <chinglinyu@xxxxxxxxxx>
>> ---
>>  fs/tracefs/Makefile      |   1 +
>>  fs/tracefs/event_inode.c | 252 +++++++++++++++++++++++++++++++++++++++
>>  include/linux/tracefs.h  |  29 +++++
>>  kernel/trace/trace.h     |   1 +
>>  4 files changed, 283 insertions(+)
>>  create mode 100644 fs/tracefs/event_inode.c
>> 
>> diff --git a/fs/tracefs/Makefile b/fs/tracefs/Makefile
>> index 7c35a282b..73c56da8e 100644
>> --- a/fs/tracefs/Makefile
>> +++ b/fs/tracefs/Makefile
>> @@ -1,5 +1,6 @@
>>  # SPDX-License-Identifier: GPL-2.0-only
>>  tracefs-objs        := inode.o
>> +tracefs-objs += event_inode.o
>> 
>>  obj-$(CONFIG_TRACING)       += tracefs.o
>> 
>> diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
>> new file mode 100644
>> index 000000000..82caba7e9
>> --- /dev/null
>> +++ b/fs/tracefs/event_inode.c
>> @@ -0,0 +1,252 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + *  event_inode.c - part of tracefs, a pseudo file system for activating tracing
>> + *
>> + *  Copyright (C) 2020-22 VMware Inc, author: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
>> + *  Copyright (C) 2020-22 VMware Inc, author: Ajay Kaher <akaher@xxxxxxxxxx>
>> + *
>> + *  eventfs is used to show trace events with one set of dentries
>> + *
>> + *  eventfs stores meta-data of files/dirs and skip to create object of
>> + *  inodes/dentries. As and when requires, eventfs will create the
>> + *  inodes/dentries for only required files/directories. Also eventfs
>> + *  would delete the inodes/dentries once no more requires but preserve
>> + *  the meta data.
>> + */
>> +#include <linux/fsnotify.h>
>> +#include <linux/fs.h>
>> +#include <linux/namei.h>
>> +#include <linux/security.h>
>> +#include <linux/tracefs.h>
>> +#include <linux/kref.h>
>> +#include <linux/delay.h>
>> +#include "internal.h"
>> +
>> +/**
>> + * eventfs_dentry_to_rwsem - Return corresponding eventfs_rwsem
>> + * @dentry: a pointer to dentry
>> + *
>> + * helper function to return crossponding eventfs_rwsem for given dentry
>> + */
>> +static struct rw_semaphore *eventfs_dentry_to_rwsem(struct dentry *dentry)
>> +{
>> +     if (S_ISDIR(dentry->d_inode->i_mode))
>> +             return (struct rw_semaphore *)dentry->d_inode->i_private;
>> +     else
>> +             return (struct rw_semaphore *)dentry->d_parent->d_inode->i_private;
>> +}
>> +
>> +/**
>> + * eventfs_down_read - acquire read lock function
>> + * @eventfs_rwsem: a pointer to rw_semaphore
>> + *
>> + * helper function to perform read lock, skip locking if caller task already
>> + * own the lock. read lock requires for lookup(), release() and these also
>> + * called with-in open(), remove() which already hold the read/write lock.
>> + */
>> +static void eventfs_down_read(struct rw_semaphore *eventfs_rwsem)
>> +{
>> +     down_read_nested(eventfs_rwsem, SINGLE_DEPTH_NESTING);
>> +}
>> +
>> +/**
>> + * eventfs_up_read - release read lock function
>> + * @eventfs_rwsem: a pointer to rw_semaphore
>> + *
>> + * helper function to release eventfs_rwsem lock if locked
>> + */
>> +static void eventfs_up_read(struct rw_semaphore *eventfs_rwsem)
>> +{
>> +     up_read(eventfs_rwsem);
>> +}
>> +
>> +/**
>> + * eventfs_down_write - acquire write lock function
>> + * @eventfs_rwsem: a pointer to rw_semaphore
>> + *
>> + * helper function to perform write lock on eventfs_rwsem
>> + */
>> +static void eventfs_down_write(struct rw_semaphore *eventfs_rwsem)
>> +{
>> +     while (!down_write_trylock(eventfs_rwsem))
>> +             msleep(10);
>> +}
>> +
>> +/**
>> + * eventfs_up_write - release write lock function
>> + * @eventfs_rwsem: a pointer to rw_semaphore
>> + *
>> + * helper function to perform write lock on eventfs_rwsem
>> + */
>> +static void eventfs_up_write(struct rw_semaphore *eventfs_rwsem)
>> +{
>> +     up_write(eventfs_rwsem);
>> +}
>> +
>> +static const struct file_operations eventfs_file_operations = {
>> +};
>> +
>> +static const struct inode_operations eventfs_root_dir_inode_operations = {
>> +};
>> +
>> +/**
>> + * eventfs_create_events_dir - create the trace event structure
>> + * @name: a pointer to a string containing the name of the directory to
>> + *        create.
>> + * @parent: a pointer to the parent dentry for this file.  This should be a
>> + *          directory dentry if set.  If this parameter is NULL, then the
>> + *          directory will be created in the root of the tracefs filesystem.
>> + * @eventfs_rwsem: a pointer to rw_semaphore
>> + *
>> + * This function creates the top of the trace event directory.
>> + */
>> +struct dentry *eventfs_create_events_dir(const char *name,
>> +                                      struct dentry *parent,
>> +                                      struct rw_semaphore *eventfs_rwsem)
>> +{
>> +     struct dentry *dentry = tracefs_start_creating(name, parent);
>> +     struct eventfs_inode *ei;
>> +     struct tracefs_inode *ti;
>> +     struct inode *inode;
>> +
>> +     if (IS_ERR(dentry))
>> +             return dentry;
>> +
>> +     ei = kzalloc(sizeof(*ei), GFP_KERNEL);
>> +     if (!ei)
>> +             return ERR_PTR(-ENOMEM);
>> +     inode = tracefs_get_inode(dentry->d_sb);
>> +     if (unlikely(!inode)) {
>> +             kfree(ei);
>> +             tracefs_failed_creating(dentry);
>> +             return ERR_PTR(-ENOMEM);
>> +     }
>> +
>> +     init_rwsem(eventfs_rwsem);
>> +     INIT_LIST_HEAD(&ei->e_top_files);
>> +
>> +     ti = get_tracefs(inode);
>> +     ti->flags |= TRACEFS_EVENT_INODE;
>> +     ti->private = ei;
>> +
>> +     inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
>> +     inode->i_op = &eventfs_root_dir_inode_operations;
>> +     inode->i_fop = &eventfs_file_operations;
>> +     inode->i_private = eventfs_rwsem;
>> +
>> +     /* directory inodes start off with i_nlink == 2 (for "." entry) */
>> +     inc_nlink(inode);
>> +     d_instantiate(dentry, inode);
>> +     inc_nlink(dentry->d_parent->d_inode);
>> +     fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
>> +     return tracefs_end_creating(dentry);
>> +}
>> +
>> +/**
>> + * eventfs_add_subsystem_dir - add eventfs subsystem_dir to list to create later
>> + * @name: a pointer to a string containing the name of the file to create.
>> + * @parent: a pointer to the parent dentry for this dir.
>> + * @eventfs_rwsem: a pointer to rw_semaphore
>> + *
>> + * This function adds eventfs subsystem dir to list.
>> + * And all these dirs are created on the fly when they are looked up,
>> + * and the dentry and inodes will be removed when they are done.
>> + */
>> +struct eventfs_file *eventfs_add_subsystem_dir(const char *name,
>> +                                            struct dentry *parent,
>> +                                            struct rw_semaphore *eventfs_rwsem)
>> +{
>> +     struct tracefs_inode *ti_parent;
>> +     struct eventfs_inode *ei_parent;
>> +     struct eventfs_file *ef;
>> +
>> +     if (!parent)
>> +             return ERR_PTR(-EINVAL);
>> +
>> +     ti_parent = get_tracefs(parent->d_inode);
>> +     ei_parent = ti_parent->private;
>> +
>> +     ef = kzalloc(sizeof(*ef), GFP_KERNEL);
>> +     if (!ef)
>> +             return ERR_PTR(-ENOMEM);
>> +
>> +     ef->ei = kzalloc(sizeof(*ef->ei), GFP_KERNEL);
>> +     if (!ef->ei) {
>> +             kfree(ef);
>> +             return ERR_PTR(-ENOMEM);
>> +     }
>> +
>> +     INIT_LIST_HEAD(&ef->ei->e_top_files);
>> +
>> +     ef->name = kstrdup(name, GFP_KERNEL);
>> +     if (!ef->name) {
>> +             kfree(ef->ei);
>> +             kfree(ef);
>> +             return ERR_PTR(-ENOMEM);
>> +     }
>> +
>> +     ef->mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
>> +     ef->iop = &eventfs_root_dir_inode_operations;
>> +     ef->fop =  &eventfs_file_operations;
>> +     ef->dentry = NULL;
>> +     ef->created = false;
>> +     ef->d_parent = parent;
>> +     ef->data = eventfs_rwsem;
>> +
>> +     eventfs_down_write(eventfs_rwsem);
>> +     list_add_tail(&ef->list, &ei_parent->e_top_files);
>> +     eventfs_up_write(eventfs_rwsem);
>> +     return ef;
>> +}
>> +
>> +/**
>> + * eventfs_add_dir - add eventfs dir to list to create later
>> + * @name: a pointer to a string containing the name of the file to create.
>> + * @ef_parent: a pointer to the parent eventfs_file for this dir.
>> + * @eventfs_rwsem: a pointer to rw_semaphore
>> + *
>> + * This function adds eventfs dir to list.
>> + * And all these dirs are created on the fly when they are looked up,
>> + * and the dentry and inodes will be removed when they are done.
>> + */
>> +struct eventfs_file *eventfs_add_dir(const char *name,
>> +                                  struct eventfs_file *ef_parent,
>> +                                  struct rw_semaphore *eventfs_rwsem)
>> +{
>> +     struct eventfs_file *ef;
>> +
>> +     if (!ef_parent)
>> +             return ERR_PTR(-EINVAL);
>> +
>> +     ef = kzalloc(sizeof(*ef), GFP_KERNEL);
>> +     if (!ef)
>> +             return ERR_PTR(-ENOMEM);
>> +
>> +     ef->ei = kzalloc(sizeof(*ef->ei), GFP_KERNEL);
>> +     if (!ef->ei) {
>> +             kfree(ef);
>> +             return ERR_PTR(-ENOMEM);
>> +     }
>> +
>> +     INIT_LIST_HEAD(&ef->ei->e_top_files);
>> +
>> +     ef->name = kstrdup(name, GFP_KERNEL);
>> +     if (!ef->name) {
>> +             kfree(ef->ei);
>> +             kfree(ef);
>> +             return ERR_PTR(-ENOMEM);
>> +     }
>> +
>> +     ef->mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
>> +     ef->iop = &eventfs_root_dir_inode_operations;
>> +     ef->fop =  &eventfs_file_operations;
>> +     ef->created = false;
>> +     ef->dentry = NULL;
>> +     ef->d_parent = NULL;
>> +     ef->data = eventfs_rwsem;
>> +
>> +     eventfs_down_write(eventfs_rwsem);
>> +     list_add_tail(&ef->list, &ef_parent->ei->e_top_files);
>> +     eventfs_up_write(eventfs_rwsem);
>> +     return ef;
>> +}
> 
> Hi,
> eventfs_add_subsystem_dir() and eventfs_add_dir() are almost the same,
> how about extract a common help function to simplify them, like:
> 
> +static struct eventfs_file *__eventfs_add_dir(const char *name,
> +                                             struct dentry *d_parent,
> +                                             struct eventfs_inode
> *ei_parent,
> +                                             struct rw_semaphore
> *eventfs_rwsem)
> +{
> +       struct eventfs_file *ef;
> +
> +       ef = kzalloc(sizeof(*ef), GFP_KERNEL);
> +       if (!ef)
> +               return ERR_PTR(-ENOMEM);
> +
> +       ef->ei = kzalloc(sizeof(*ef->ei), GFP_KERNEL);
> +       if (!ef->ei) {
> +               kfree(ef);
> +               return ERR_PTR(-ENOMEM);
> +       }
> +
> +       INIT_LIST_HEAD(&ef->ei->e_top_files);
> +
> +       ef->name = kstrdup(name, GFP_KERNEL);
> +       if (!ef->name) {
> +               kfree(ef->ei);
> +               kfree(ef);
> +               return ERR_PTR(-ENOMEM);
> +       }
> +
> +       ef->mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
> +       ef->iop = &eventfs_root_dir_inode_operations;
> +       ef->fop = &eventfs_file_operations;
> +       ef->dentry = NULL;
> +       ef->created = false;
> +       ef->d_parent = d_parent;
> +       ef->data = eventfs_rwsem;
> +
> +       eventfs_down_write(eventfs_rwsem);
> +       list_add_tail(&ef->list, &ei_parent->e_top_files);
> +       eventfs_up_write(eventfs_rwsem);
> +       return ef;
> +}
> +
> +struct eventfs_file *eventfs_add_subsystem_dir(const char *name,
> +                                              struct dentry *parent,
> +                                              struct rw_semaphore
> *eventfs_rwsem)
> +{
> +       struct tracefs_inode *ti_parent;
> +       struct eventfs_inode *ei_parent;
> +
> +       if (!parent)
> +               return ERR_PTR(-EINVAL);
> +       ti_parent = get_tracefs(parent->d_inode);
> +       ei_parent = ti_parent->private;
> +       return __eventfs_add_dir(name, parent, ei_parent, eventfs_rwsem);
> +}
> +
> +struct eventfs_file *eventfs_add_dir(const char *name,
> +                                    struct eventfs_file *ef_parent,
> +                                    struct rw_semaphore *eventfs_rwsem)
> +{
> +       if (!ef_parent)
> +               return ERR_PTR(-EINVAL);
> +       return __eventfs_add_dir(name, NULL, ef_parent->ei, eventfs_rwsem);
> +}

Sounds good. Thanks for sharing code snippet. I will consider in v3.

- Ajay

>> diff --git a/include/linux/tracefs.h b/include/linux/tracefs.h
>> index 999124459..aeca6761f 100644
>> --- a/include/linux/tracefs.h
>> +++ b/include/linux/tracefs.h
>> @@ -21,6 +21,35 @@ struct file_operations;
>> 
>>  #ifdef CONFIG_TRACING
>> 
>> +struct eventfs_inode {
>> +     struct list_head                e_top_files;
>> +};
>> +
>> +struct eventfs_file {
>> +     const char                      *name;
>> +     struct dentry                   *d_parent;
>> +     struct dentry                   *dentry;
>> +     struct list_head                list;
>> +     struct eventfs_inode            *ei;
>> +     const struct file_operations    *fop;
>> +     const struct inode_operations   *iop;
>> +     void                            *data;
>> +     umode_t                         mode;
>> +     bool                            created;
>> +};
>> +
>> +struct dentry *eventfs_create_events_dir(const char *name,
>> +                                      struct dentry *parent,
>> +                                      struct rw_semaphore *eventfs_rwsem);
>> +
>> +struct eventfs_file *eventfs_add_subsystem_dir(const char *name,
>> +                                            struct dentry *parent,
>> +                                            struct rw_semaphore *eventfs_rwsem);
>> +
>> +struct eventfs_file *eventfs_add_dir(const char *name,
>> +                                  struct eventfs_file *ef_parent,
>> +                                  struct rw_semaphore *eventfs_rwsem);
>> +
>>  struct dentry *tracefs_create_file(const char *name, umode_t mode,
>>                                 struct dentry *parent, void *data,
>>                                 const struct file_operations *fops);
>> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
>> index 616e1aa1c..3726725c8 100644
>> --- a/kernel/trace/trace.h
>> +++ b/kernel/trace/trace.h
>> @@ -359,6 +359,7 @@ struct trace_array {
>>      struct dentry           *options;
>>      struct dentry           *percpu_dir;
>>      struct dentry           *event_dir;
>> +     struct rw_semaphore     eventfs_rwsem;
>>      struct trace_options    *topts;
>>      struct list_head        systems;
>>      struct list_head        events;