Re: [f2fs-dev] [PATCH RESEND 5/5] f2fs: add ioctl to export read extent cache to userspace for debug

On 6/20/26 3:05 PM, Chao Yu via Linux-f2fs-devel wrote:
> On 6/19/26 22:56, Yongpeng Yang wrote:
>>
>> On 6/15/26 11:51 PM, Jaegeuk Kim via Linux-f2fs-devel wrote:
>>> On 06/15, Chao Yu via Linux-f2fs-devel wrote:
>>>> On 6/12/26 19:58, Yongpeng Yang wrote:
>>>>> From: Yongpeng Yang <[email protected]>
>>>>>
>>>>> Add F2FS_IOC_GET_READ_CACHE_EXTENTS ioctl that allows userspace to
>>>>> retrieve all cached read extents for a given file. This uses a two- 
>>>>> call
>>>>> pattern similar to fiemap: the first call with ext_count=0 queries the
>>>>> node_count, and the second call fetches the actual extent entries.
>>>>
>>>> It looks a little bit heavy to maintain a debug purpose ioctl 
>>>> interface.
>>>>
>>>> Maybe set ino via sysfs and dump extent cache via procfs? only enabled
>>>> if F2FS_CHECK_FS=y?
>>>>
>>>> Jaegeuk, do you have any suggestion?
>>>
>>> Agreed, and even not sure we need sysfs or procfs. Can we dump the 
>>> extents
>>> via fsck?
>>
>> It is indeed quite heavy. Our primary goal here is debugging inode
>> extent trees, and fsck cannot meet this requirement. If we rely on
>> procfs or sysfs interfaces, we would have to open dedicated files within
>> sysfs.c, which feels like an inappropriate approach.
> 
> call access() in userspace application or touch in script to load inode via
> lookup() first, then access sysfs and procfs node?

Thanks for the suggestion, this is more lightweight. I'll modify it in
v2 patch.

Thanks
Yongpeng,

> 
> Thanks,
> 
>>
>> Thanks
>> Yongpeng,
>>
>>>
>>>>
>>>> Thanks,
>>>>
>>>>>
>>>>> Signed-off-by: Yongpeng Yang <[email protected]>
>>>>> ---
>>>>>   fs/f2fs/extent_cache.c    | 70 ++++++++++++++++++++++++++++++++++ 
>>>>> +++++
>>>>>   fs/f2fs/f2fs.h            |  3 ++
>>>>>   fs/f2fs/file.c            | 11 ++++++
>>>>>   include/uapi/linux/f2fs.h | 21 ++++++++++++
>>>>>   4 files changed, 105 insertions(+)
>>>>>
>>>>> diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c
>>>>> index e141ffb64e5f..0c10d5639d68 100644
>>>>> --- a/fs/f2fs/extent_cache.c
>>>>> +++ b/fs/f2fs/extent_cache.c
>>>>> @@ -14,6 +14,7 @@
>>>>>   #include <linux/fs.h>
>>>>>   #include <linux/f2fs_fs.h>
>>>>> +#include <uapi/linux/f2fs.h>
>>>>>   #include "f2fs.h"
>>>>>   #include "node.h"
>>>>> @@ -1267,6 +1268,75 @@ static void __init_extent_tree_info(struct 
>>>>> extent_tree_info *eti)
>>>>>       atomic_set(&eti->total_ext_node, 0);
>>>>>   }
>>>>> +int f2fs_get_read_cache_extents(struct inode *inode,
>>>>> +            struct f2fs_read_cache_extent __user *uarg)
>>>>> +{
>>>>> +    struct extent_tree *et = F2FS_I(inode)->extent_tree[EX_READ];
>>>>> +    struct f2fs_cache_extent_info *kbuf = NULL;
>>>>> +    struct f2fs_cache_extent_info largest = {};
>>>>> +    struct rb_node *node;
>>>>> +    struct extent_node *en;
>>>>> +    unsigned int capacity, count = 0;
>>>>> +    __u32 flags = 0;
>>>>> +    int ret = 0;
>>>>> +
>>>>> +    if (get_user(capacity, &uarg->ext_count))
>>>>> +        return -EFAULT;
>>>>> +
>>>>> +    if (is_inode_flag_set(inode, FI_NO_EXTENT))
>>>>> +        flags |= F2FS_EXT_FL_NO_EXTENT;
>>>>> +
>>>>> +    if (!et || (flags & F2FS_EXT_FL_NO_EXTENT)) {
>>>>> +        if (put_user(0U, &uarg->ext_count) ||
>>>>> +            put_user(flags, &uarg->flags) ||
>>>>> +            put_user(0U, &uarg->node_count))
>>>>> +            return -EFAULT;
>>>>> +        return 0;
>>>>> +    }
>>>>> +
>>>>> +    if (capacity) {
>>>>> +        kbuf = f2fs_kvmalloc(F2FS_I_SB(inode), capacity * 
>>>>> sizeof(*kbuf), GFP_KERNEL);
>>>>> +        if (!kbuf)
>>>>> +            return -ENOMEM;
>>>>> +    }
>>>>> +
>>>>> +    read_lock(&et->lock);
>>>>> +
>>>>> +    largest.fofs = et->largest.fofs;
>>>>> +    largest.blk = et->largest.blk;
>>>>> +    largest.len = et->largest.len;
>>>>> +    largest.last_access_mode = et->largest.last_access_mode;
>>>>> +
>>>>> +    for (node = rb_first_cached(&et->root); node; node = 
>>>>> rb_next(node)) {
>>>>> +        if (count >= capacity)
>>>>> +            break;
>>>>> +        en = rb_entry(node, struct extent_node, rb_node);
>>>>> +
>>>>> +        kbuf[count].fofs = en->ei.fofs;
>>>>> +        kbuf[count].blk = en->ei.blk;
>>>>> +        kbuf[count].len = en->ei.len;
>>>>> +        kbuf[count].last_access_mode = en->ei.last_access_mode;
>>>>> +        count++;
>>>>> +    }
>>>>> +
>>>>> +    read_unlock(&et->lock);
>>>>> +
>>>>> +    if (count && copy_to_user(uarg->extents, kbuf,
>>>>> +                  count * sizeof(*kbuf))) {
>>>>> +        ret = -EFAULT;
>>>>> +        goto out;
>>>>> +    }
>>>>> +
>>>>> +    if (put_user(count, &uarg->ext_count) ||
>>>>> +        put_user(flags, &uarg->flags) ||
>>>>> +        put_user((u32)atomic_read(&et->node_cnt), &uarg- 
>>>>> >node_count) ||
>>>>> +        copy_to_user(&uarg->largest, &largest, sizeof(largest)))
>>>>> +        ret = -EFAULT;
>>>>> +out:
>>>>> +    kvfree(kbuf);
>>>>> +    return ret;
>>>>> +}
>>>>> +
>>>>>   void f2fs_init_extent_cache_info(struct f2fs_sb_info *sbi)
>>>>>   {
>>>>>       __init_extent_tree_info(&sbi->extent_tree[EX_READ]);
>>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>>> index 1588b64d04a3..69641fc31c51 100644
>>>>> --- a/fs/f2fs/f2fs.h
>>>>> +++ b/fs/f2fs/f2fs.h
>>>>> @@ -26,6 +26,7 @@
>>>>>   #include <linux/part_stat.h>
>>>>>   #include <linux/rw_hint.h>
>>>>> +#include <uapi/linux/f2fs.h>
>>>>>   #include <linux/fscrypt.h>
>>>>>   #include <linux/fsverity.h>
>>>>> @@ -4590,6 +4591,8 @@ void f2fs_update_read_extent_cache(struct 
>>>>> dnode_of_data *dn);
>>>>>   void f2fs_update_read_extent_cache_range(struct dnode_of_data *dn,
>>>>>                   pgoff_t fofs, block_t blkaddr, unsigned int len,
>>>>>                   enum extent_access_mode access_mode);
>>>>> +int f2fs_get_read_cache_extents(struct inode *inode,
>>>>> +            struct f2fs_read_cache_extent __user *uarg);
>>>>>   unsigned int f2fs_shrink_read_extent_tree(struct f2fs_sb_info *sbi,
>>>>>               int nr_shrink);
>>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>>>> index a3a5d499eadf..66ec9927d667 100644
>>>>> --- a/fs/f2fs/file.c
>>>>> +++ b/fs/f2fs/file.c
>>>>> @@ -3672,6 +3672,14 @@ static int f2fs_ioc_precache_extents(struct 
>>>>> file *filp)
>>>>>       return f2fs_precache_extents(file_inode(filp));
>>>>>   }
>>>>> +static int f2fs_ioc_get_read_cache_extents(struct file *filp, 
>>>>> unsigned long arg)
>>>>> +{
>>>>> +    struct inode *inode = file_inode(filp);
>>>>> +
>>>>> +    return f2fs_get_read_cache_extents(inode,
>>>>> +            (struct f2fs_read_cache_extent __user *)arg);
>>>>> +}
>>>>> +
>>>>>   static int f2fs_ioc_resize_fs(struct file *filp, unsigned long arg)
>>>>>   {
>>>>>       struct f2fs_sb_info *sbi = F2FS_I_SB(file_inode(filp));
>>>>> @@ -4744,6 +4752,8 @@ static long __f2fs_ioctl(struct file *filp, 
>>>>> unsigned int cmd, unsigned long arg)
>>>>>           return f2fs_ioc_get_dev_alias_file(filp, arg);
>>>>>       case F2FS_IOC_IO_PRIO:
>>>>>           return f2fs_ioc_io_prio(filp, arg);
>>>>> +    case F2FS_IOC_GET_READ_CACHE_EXTENTS:
>>>>> +        return f2fs_ioc_get_read_cache_extents(filp, arg);
>>>>>       default:
>>>>>           return -ENOTTY;
>>>>>       }
>>>>> @@ -5506,6 +5516,7 @@ long f2fs_compat_ioctl(struct file *file, 
>>>>> unsigned int cmd, unsigned long arg)
>>>>>       case F2FS_IOC_COMPRESS_FILE:
>>>>>       case F2FS_IOC_GET_DEV_ALIAS_FILE:
>>>>>       case F2FS_IOC_IO_PRIO:
>>>>> +    case F2FS_IOC_GET_READ_CACHE_EXTENTS:
>>>>>           break;
>>>>>       default:
>>>>>           return -ENOIOCTLCMD;
>>>>> diff --git a/include/uapi/linux/f2fs.h b/include/uapi/linux/f2fs.h
>>>>> index 795e26258355..6ff9003bc030 100644
>>>>> --- a/include/uapi/linux/f2fs.h
>>>>> +++ b/include/uapi/linux/f2fs.h
>>>>> @@ -45,6 +45,8 @@
>>>>>   #define F2FS_IOC_START_ATOMIC_REPLACE    _IO(F2FS_IOCTL_MAGIC, 25)
>>>>>   #define F2FS_IOC_GET_DEV_ALIAS_FILE    _IOR(F2FS_IOCTL_MAGIC, 26, 
>>>>> __u32)
>>>>>   #define F2FS_IOC_IO_PRIO        _IOW(F2FS_IOCTL_MAGIC, 27, __u32)
>>>>> +#define F2FS_IOC_GET_READ_CACHE_EXTENTS    _IOWR(F2FS_IOCTL_MAGIC, 
>>>>> 28,    \
>>>>> +                        struct f2fs_read_cache_extent)
>>>>>   /*
>>>>>    * should be same as XFS_IOC_GOINGDOWN.
>>>>> @@ -104,4 +106,23 @@ struct f2fs_comp_option {
>>>>>       __u8 log_cluster_size;
>>>>>   };
>>>>> +struct f2fs_cache_extent_info {
>>>>> +    __u32 fofs;        /* start file offset in blocks */
>>>>> +    __u32 blk;        /* start block address */
>>>>> +    __u32 len;        /* length in blocks */
>>>>> +    __u32 last_access_mode; /* last access mode of extent_node */
>>>>> +};
>>>>> +
>>>>> +/* flags for f2fs_read_cache_extent */
>>>>> +#define F2FS_EXT_FL_NO_EXTENT    0x1    /* extent cache disabled 
>>>>> for this inode */
>>>>> +
>>>>> +struct f2fs_read_cache_extent {
>>>>> +    __u32 ext_count;    /* in: array capacity; out: mapped extent 
>>>>> count */
>>>>> +    __u32 flags;        /* out: status flags */
>>>>> +    __u32 node_count;    /* out: total extent nodes in tree */
>>>>> +    __u32 reserved;
>>>>> +    struct f2fs_cache_extent_info largest;        /* out: largest 
>>>>> extent */
>>>>> +    struct f2fs_cache_extent_info extents[];    /* out: extent 
>>>>> array */
>>>>> +};
>>>>> +
>>>>>   #endif /* _UAPI_LINUX_F2FS_H */
>>>>
>>>>
>>>>
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>>>
>>>
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>>
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