[PATCH 1/1] loop: sync filesystem cache before getting file size in get_size()

[PATCH 1/1] loop: sync filesystem cache before getting file size in get_size()

[Rajeev Mishra]

The get_size() function now uses vfs_getattr_nosec() with AT_STATX_SYNC_AS_STAT
to ensure filesystem cache is synchronized before retrieving file size. This
provides more accurate size information, especially when:

- The backing file size has been changed by another process
- The file is on a network filesystem (NFS, CIFS, etc.)
- The file is being modified concurrently
- The most accurate size is needed for loop device setup

The implementation gracefully falls back to i_size_read() if vfs_getattr_nosec()
fails, maintaining backward compatibility.

Signed-off-by: Rajeev Mishra <rajeevm@hpe.com>
---
 drivers/block/loop.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 1b6ee91f8eb9..15d5edbc69ce 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -137,12 +137,39 @@ static void loop_global_unlock(struct loop_device *lo, bool global)
 static int max_part;
 static int part_shift;
 
+/**
+ * get_size - calculate the effective size of a loop device
+ * @offset: offset into the backing file
+ * @sizelimit: user-specified size limit
+ * @file: the backing file
+ *
+ * Calculate the effective size of the loop device
+ *
+ * Returns: size in 512-byte sectors, or 0 if invalid
+ */
 static loff_t get_size(loff_t offset, loff_t sizelimit, struct file *file)
 {
+	struct kstat stat;
 	loff_t loopsize;
+	int ret;
+
+	/*
+	 * Get file attributes for validation. We use vfs_getattr() to ensure
+	 * we have up-to-date file size information.
+	 */
+	ret = vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE, 
+			        AT_STATX_SYNC_AS_STAT);
+	if (ret) {
+		/*
+		 * If we can't get attributes, fall back to i_size_read()
+		 * which should work for most cases.
+		 */
+		loopsize = i_size_read(file->f_mapping->host);
+	} else {
+		/* Use the size from getattr for consistency */
+		loopsize = stat.size;
+	}
 
-	/* Compute loopsize in bytes */
-	loopsize = i_size_read(file->f_mapping->host);
 	if (offset > 0)
 		loopsize -= offset;
 	/* offset is beyond i_size, weird but possible */
-- 
2.43.5

Re: [PATCH 1/1] loop: sync filesystem cache before getting file size in get_size()

[Yu Kuai]

Hi,

在 2025/08/08 7:25, Rajeev Mishra 写道:
> The get_size() function now uses vfs_getattr_nosec() with AT_STATX_SYNC_AS_STAT

With a quick code review, I didn't found how can that flag ensure
filesystem cache is synchronized, can you explain in detail? Or Do you
mean getattr for filesystem like fuse to get latest data from server?

> to ensure filesystem cache is synchronized before retrieving file size. This
> provides more accurate size information, especially when:
> 
> - The backing file size has been changed by another process
> - The file is on a network filesystem (NFS, CIFS, etc.)
> - The file is being modified concurrently

I don't think this make sense in real world. If a file is already used
by loop device, then user should avoid modifying this file directly. For
a file in fuse, I feel it's not good to use it as loop device.

> - The most accurate size is needed for loop device setup
> > The implementation gracefully falls back to i_size_read() if 
vfs_getattr_nosec()
> fails, maintaining backward compatibility.
> 
> Signed-off-by: Rajeev Mishra <rajeevm@hpe.com>
> ---
>   drivers/block/loop.c | 31 +++++++++++++++++++++++++++++--
>   1 file changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 1b6ee91f8eb9..15d5edbc69ce 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -137,12 +137,39 @@ static void loop_global_unlock(struct loop_device *lo, bool global)
>   static int max_part;
>   static int part_shift;
>   
> +/**
> + * get_size - calculate the effective size of a loop device
> + * @offset: offset into the backing file
> + * @sizelimit: user-specified size limit
> + * @file: the backing file
> + *
> + * Calculate the effective size of the loop device
> + *
> + * Returns: size in 512-byte sectors, or 0 if invalid
> + */
>   static loff_t get_size(loff_t offset, loff_t sizelimit, struct file *file)
>   {
> +	struct kstat stat;
>   	loff_t loopsize;
> +	int ret;
> +
> +	/*
> +	 * Get file attributes for validation. We use vfs_getattr() to ensure
> +	 * we have up-to-date file size information.
> +	 */
> +	ret = vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE,
> +			        AT_STATX_SYNC_AS_STAT);
> +	if (ret) {
> +		/*
> +		 * If we can't get attributes, fall back to i_size_read()
> +		 * which should work for most cases.
> +		 */
> +		loopsize = i_size_read(file->f_mapping->host);
> +	} else {
> +		/* Use the size from getattr for consistency */
> +		loopsize = stat.size;
> +	}

I'm ok switch from i_size_read() to getattr, however, the commit message
is confusing for me :(

Thanks,
Kuai
>   
> -	/* Compute loopsize in bytes */
> -	loopsize = i_size_read(file->f_mapping->host);
>   	if (offset > 0)
>   		loopsize -= offset;
>   	/* offset is beyond i_size, weird but possible */
> 

Re: [PATCH 1/1] loop: sync filesystem cache before getting file size in get_size()

[Yu Kuai]

Hi,

在 2025/08/09 2:50, Mishra, Rajeev 写道:
> Thanks, Kuai, for the quick review — I really appreciate it. Please let me know if you have any questions or if I missed addressing anything.
> My response to queries is inline below.
> Rajeev
> 
> From: Yu Kuai <yukuai1@huaweicloud.com>
> Date: Thursday, August 7, 2025 at 9:48 PM
> To: Mishra, Rajeev <rajeevm@hpe.com>, axboe@kernel.dk <axboe@kernel.dk>
> Cc: linux-block@vger.kernel.org <linux-block@vger.kernel.org>, linux-kernel@vger.kernel.org <linux-kernel@vger.kernel.org>, yukuai (C) <yukuai3@huawei.com>
> Subject: Re: [PATCH 1/1] loop: sync filesystem cache before getting file size in get_size()
> Hi,
> 
> 在 2025/08/08 7:25, Rajeev Mishra 写道:
>> The get_size() function now uses vfs_getattr_nosec() with AT_STATX_SYNC_AS_STAT
> 
> With a quick code review, I didn't found how can that flag ensure
> filesystem cache is synchronized, can you explain in detail? Or Do you
> mean getattr for filesystem like fuse to get latest data from server?
> Response ---
>>> Thanks for the quick review. The AT_STATX_SYNC_AS_STAT flag tells
>>> the VFS layer to synchronize cached metadata before returning file attributes.
>>> This is particularly important for distributed/network filesystems where
>>> the local cache may not reflect the current file size on the server.
> ---

I think this is the default behavior, unless AT_STATX_DONT_SYNC is set.
So I think you don't need to emphasize the flag AT_STATX_SYNC_AS_STAT,
otherwise, at least I will think if the flag is not set, cache won't be
synchronized.

> 
>> to ensure filesystem cache is synchronized before retrieving file size. This
>> provides more accurate size information, especially when:
>>
>> - The backing file size has been changed by another process
>> - The file is on a network filesystem (NFS, CIFS, etc.)
>> - The file is being modified concurrently
> 
> I don't think this make sense in real world. If a file is already used
> by loop device, then user should avoid modifying this file directly. For
> a file in fuse, I feel it's not good to use it as loop device.
> Response---
>>> I encountered this issue specifically with Lustre filesystem during testing
>>> I did following --
>>> 1. File was created on Lustre
>>> 2. dd was done to write data on the file
>>> 3. ls confirmed the size
>>> 4. Loop device setup was done on the file immediately
>>> 5. write was issued with less space
>>> 6.above happened as file size was not correctly captured by loop device
> 
>>> I agree that network/distributed filesystems aren't ideal for loop devices,
>>> but they are used in practice (container images on shared storage, diskless
>>> systems, etc.). The fallback to i_size_read() ensures no performance penalty
>>> for local filesystems while improving reliability for network filesystems.

Ok, I agree with this case, can you please just keep the network
filesystem, and remove the description about concurrent modifying of
loop file?

> ____
> 
>> - The most accurate size is needed for loop device setup
>>> The implementation gracefully falls back to i_size_read() if
> vfs_getattr_nosec()
>> fails, maintaining backward compatibility.
> Response –
> ___
>>>> you mean using the flag sync has backward compatibility issue ? or using function itself ?

Nevermind, this is from your orginal patch, I somehow added a new line
break.
> ___
> 
>>>
>> Signed-off-by: Rajeev Mishra <rajeevm@hpe.com>
>> ---
>>    drivers/block/loop.c | 31 +++++++++++++++++++++++++++++--
>>    1 file changed, 29 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
>> index 1b6ee91f8eb9..15d5edbc69ce 100644
>> --- a/drivers/block/loop.c
>> +++ b/drivers/block/loop.c
>> @@ -137,12 +137,39 @@ static void loop_global_unlock(struct loop_device *lo, bool global)
>>    static int max_part;
>>    static int part_shift;
>>
>> +/**
>> + * get_size - calculate the effective size of a loop device
>> + * @offset: offset into the backing file
>> + * @sizelimit: user-specified size limit
>> + * @file: the backing file
>> + *
>> + * Calculate the effective size of the loop device
>> + *
>> + * Returns: size in 512-byte sectors, or 0 if invalid
>> + */
>>    static loff_t get_size(loff_t offset, loff_t sizelimit, struct file *file)
>>    {
>> +     struct kstat stat;
>>         loff_t loopsize;
>> +     int ret;
>> +
>> +     /*
>> +      * Get file attributes for validation. We use vfs_getattr() to ensure
>> +      * we have up-to-date file size information.
>> +      */
>> +     ret = vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE,
>> +                             AT_STATX_SYNC_AS_STAT);
>> +     if (ret) {
>> +             /*
>> +              * If we can't get attributes, fall back to i_size_read()
>> +              * which should work for most cases.
>> +              */
>> +             loopsize = i_size_read(file->f_mapping->host);
>> +     } else {
>> +             /* Use the size from getattr for consistency */
>> +             loopsize = stat.size;
>> +     }
> 
> I'm ok switch from i_size_read() to getattr, however, the commit message
> is confusing for me :(
> 
> Response --
>>> I will make the commit message clear and simple. Just wanted to understand
>>> if using this will be good “vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE, 0);”
>>> is good I will replace i_size_read() with above code
>>> do let me know if this will have any backward compatibility issue
>>> Thanks again for your help

I'm good, and i_size_read() is not needed anymore.

Thanks,
Kuai

> 
> 
> Thanks,
> Kuai
>>
>> -     /* Compute loopsize in bytes */
>> -     loopsize = i_size_read(file->f_mapping->host);
>>         if (offset > 0)
>>                 loopsize -= offset;
>>         /* offset is beyond i_size, weird but possible */
>>

Re: [PATCH 1/1] loop: sync filesystem cache before getting file size in get_size()

[Christoph Hellwig]

On Thu, Aug 07, 2025 at 11:25:22PM +0000, Rajeev Mishra wrote:
> The get_size() function now uses vfs_getattr_nosec() with AT_STATX_SYNC_AS_STAT
> to ensure filesystem cache is synchronized before retrieving file size. This
> provides more accurate size information, especially when:
> 
> - The backing file size has been changed by another process
> - The file is on a network filesystem (NFS, CIFS, etc.)
> - The file is being modified concurrently
> - The most accurate size is needed for loop device setup
> 

Please wrap your commit messages at 73 (or apparently 75) lines.

Also 'syncing the cache' (what cache?) is at best an implementation
detail.  The VFS semantics simply are that you need a getattr to
retrieve the inode size, and the loop code fails to do this correctly.

> The implementation gracefully falls back to i_size_read() if vfs_getattr_nosec()
> fails, maintaining backward compatibility.

No need to fall back.  If vfs_getattr faills the file systems is
completely toast.

>  static int part_shift;
>  
> +/**
> + * get_size - calculate the effective size of a loop device
> + * @offset: offset into the backing file
> + * @sizelimit: user-specified size limit
> + * @file: the backing file
> + *
> + * Calculate the effective size of the loop device
> + *
> + * Returns: size in 512-byte sectors, or 0 if invalid
> + */

We don't really need a verbose kerneldoc for a static helper with 2
callers.

>  static loff_t get_size(loff_t offset, loff_t sizelimit, struct file *file)
>  {
> +	struct kstat stat;
>  	loff_t loopsize;
> +	int ret;
> +
> +	/*
> +	 * Get file attributes for validation. We use vfs_getattr() to ensure
> +	 * we have up-to-date file size information.
> +	 */

The comment seems a bit misleading or at least not to the point.

I'd say:

	/*
	 * File systems don't have to keep i_size in sync.  While local file
	 * systems typically keep it in sync, remote file system often do not.
	 * Go through ->getattr to retrieve the current value.
	 */

> +	ret = vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE, 
> +			        AT_STATX_SYNC_AS_STAT);

Most kernel callers just pass 0 instead of AT_STATX_SYNC_AS_STAT here,
which honestly is less confusing as I had to look up
AT_STATX_SYNC_AS_STAT first.

> +	if (ret) {
> +		/*
> +		 * If we can't get attributes, fall back to i_size_read()
> +		 * which should work for most cases.
> +		 */

As said above, there is no need to do this.  Adding a proper error
return chain here is better.

Re: [PATCH 1/1] loop: sync filesystem cache before getting file size in get_size()

[kernel test robot]

Hello,

kernel test robot noticed "blktests.loop/004.fail" on:

commit: 081158bd768a2a4b4fc6108abc3d4ee51bfdbf6e ("[PATCH 1/1] loop: sync filesystem cache before getting file size in get_size()")
url: https://github.com/intel-lab-lkp/linux/commits/Rajeev-Mishra/loop-sync-filesystem-cache-before-getting-file-size-in-get_size/20250808-073617
base: https://git.kernel.org/cgit/linux/kernel/git/axboe/linux-block.git for-next
patch link: https://lore.kernel.org/all/20250807232522.192898-1-rajeevm@hpe.com/
patch subject: [PATCH 1/1] loop: sync filesystem cache before getting file size in get_size()

in testcase: blktests
version: blktests-x86_64-a08678c-1_20250813
with following parameters:

	test: loop-004



config: x86_64-rhel-9.4-func
compiler: gcc-12
test machine: 4 threads Intel(R) Core(TM) i5-6500 CPU @ 3.20GHz (Skylake) with 32G memory

(please refer to attached dmesg/kmsg for entire log/backtrace)



If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <oliver.sang@intel.com>
| Closes: https://lore.kernel.org/oe-lkp/202508150425.33b5498e-lkp@intel.com

2025-08-14 08:21:17 echo loop/004
2025-08-14 08:21:17 ./check loop/004
loop/004 (combine loop direct I/O mode and a custom block size)
loop/004 (combine loop direct I/O mode and a custom block size) [failed]
    runtime    ...  0.668s
    --- tests/loop/004.out	2025-08-13 07:46:30.000000000 +0000
    +++ /lkp/benchmarks/blktests/results/nodev/loop/004.out.bad	2025-08-14 08:21:18.595234684 +0000
    @@ -1,4 +1,5 @@
     Running loop/004
     1
    -769bd186841c10e5b1106b55986206c0e87fc05a7f565fdee01b5abcaff6ae78  -
    +pwrite: No space left on device
    +e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855  -
     Test complete



The kernel config and materials to reproduce are available at:
https://download.01.org/0day-ci/archive/20250815/202508150425.33b5498e-lkp@intel.com



-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH 1/1] loop: sync filesystem cache before getting file size in get_size()

[Cloud User]

Thanks, Kuai, for the quick review—I really appreciate it.
Please feel free to reach out if you have any questions or
if I missed addressing anything.

My responses to your queries are included inline below.
Rajeev
 
From: Yu Kuai <yukuai1@huaweicloud.com>
Date: Thursday, August 7, 2025 at 9:48 PM
To: Mishra, Rajeev <rajeevm@hpe.com>, axboe@kernel.dk <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org <linux-block@vger.kernel.org>, linux-kernel@vger.kernel.org <linux-kernel@vger.kernel.org>, yukuai (C) <yukuai3@huawei.com>
Subject: Re: [PATCH 1/1] loop: sync filesystem cache before getting file size in get_size()

Hi,

在 2025/08/08 7:25, Rajeev Mishra 写道:
> The get_size() function now uses vfs_getattr_nosec() with AT_STATX_SYNC_AS_STAT

With a quick code review, I didn't found how can that flag ensure
filesystem cache is synchronized, can you explain in detail? Or Do you
mean getattr for filesystem like fuse to get latest data from server?

Response ---

>> Thanks for the quick review. The AT_STATX_SYNC_AS_STAT flag tells

>>the VFS layer to synchronize cached metadata before returning file attributes.

>>This is particularly important for distributed/network filesystems where

>>the local cache may not reflect the current file size on the server.

---

> to ensure filesystem cache is synchronized before retrieving file size. This
> provides more accurate size information, especially when:
>
> - The backing file size has been changed by another process
> - The file is on a network filesystem (NFS, CIFS, etc.)
> - The file is being modified concurrently

I don't think this make sense in real world. If a file is already used
by loop device, then user should avoid modifying this file directly. For
a file in fuse, I feel it's not good to use it as loop device.

Response---

>>I encountered this issue specifically with Lustre filesystem during testing
>> I did following --

>>1. File was created on Lustre

>>2. dd was done to write data on the file

>>3. ls confirmed the size

>>4. Loop device setup was done on the file immediately

>>5. write was issued with less space

>>6.above happened as file size was not correctly captured by loop device

>>I agree that network/distributed filesystems aren't ideal for loop devices,

>>but they are used in practice (container images on shared storage, diskless

>>systems, etc.). The fallback to i_size_read() ensures no performance penalty

>>for local filesystems while improving reliability for network filesystems.

____


> - The most accurate size is needed for loop device setup
> > The implementation gracefully falls back to i_size_read() if
vfs_getattr_nosec()
> fails, maintaining backward compatibility.

Response –

___

>>> you mean using the flag sync has backward compatibility issue ? or using function itself ?

___


>>
> Signed-off-by: Rajeev Mishra <rajeevm@hpe.com>
> ---
>   drivers/block/loop.c | 31 +++++++++++++++++++++++++++++--
>   1 file changed, 29 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 1b6ee91f8eb9..15d5edbc69ce 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -137,12 +137,39 @@ static void loop_global_unlock(struct loop_device *lo, bool global)
>   static int max_part;
>   static int part_shift;
>  
> +/**
> + * get_size - calculate the effective size of a loop device
> + * @offset: offset into the backing file
> + * @sizelimit: user-specified size limit
> + * @file: the backing file
> + *
> + * Calculate the effective size of the loop device
> + *
> + * Returns: size in 512-byte sectors, or 0 if invalid
> + */
>   static loff_t get_size(loff_t offset, loff_t sizelimit, struct file *file)
>   {
> +     struct kstat stat;
>        loff_t loopsize;
> +     int ret;
> +
> +     /*
> +      * Get file attributes for validation. We use vfs_getattr() to ensure
> +      * we have up-to-date file size information.
> +      */
> +     ret = vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE,
> +                             AT_STATX_SYNC_AS_STAT);
> +     if (ret) {
> +             /*
> +              * If we can't get attributes, fall back to i_size_read()
> +              * which should work for most cases.
> +              */
> +             loopsize = i_size_read(file->f_mapping->host);
> +     } else {
> +             /* Use the size from getattr for consistency */
> +             loopsize = stat.size;
> +     }

I'm ok switch from i_size_read() to getattr, however, the commit message
is confusing for me :(


Response --
>> I will make the commit message clear and simple. Just wanted to understand

>> if using this will be good “vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE, 0);”

>> is good I will replace i_size_read() with above code

>> do let me know if this will have any backward compatibility issue

>>Thanks again for your help

 


Thanks,
Kuai
>  
> -     /* Compute loopsize in bytes */
> -     loopsize = i_size_read(file->f_mapping->host);
>        if (offset > 0)
>                loopsize -= offset;
>        /* offset is beyond i_size, weird but possible */
>

Re: [PATCH 1/1] loop: sync filesystem cache before getting file size in get_size()

[Cloud User]

Thanks, Kuai, for the quick review—I really appreciate it.
Please feel free to reach out if you have any questions or
if I missed addressing anything.

My responses to your queries are included inline below.
Rajeev
 
From: Yu Kuai <yukuai1@huaweicloud.com>
Date: Thursday, August 7, 2025 at 9:48 PM
To: Mishra, Rajeev <rajeevm@hpe.com>, axboe@kernel.dk <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org <linux-block@vger.kernel.org>, linux-kernel@vger.kernel.org <linux-kernel@vger.kernel.org>, yukuai (C) <yukuai3@huawei.com>
Subject: Re: [PATCH 1/1] loop: sync filesystem cache before getting file size in get_size()

Hi,

在 2025/08/08 7:25, Rajeev Mishra 写道:
> The get_size() function now uses vfs_getattr_nosec() with AT_STATX_SYNC_AS_STAT

With a quick code review, I didn't found how can that flag ensure
filesystem cache is synchronized, can you explain in detail? Or Do you
mean getattr for filesystem like fuse to get latest data from server?

Response ---

>> Thanks for the quick review. The AT_STATX_SYNC_AS_STAT flag tells

>>the VFS layer to synchronize cached metadata before returning file attributes.

>>This is particularly important for distributed/network filesystems where

>>the local cache may not reflect the current file size on the server.

---

> to ensure filesystem cache is synchronized before retrieving file size. This
> provides more accurate size information, especially when:
>
> - The backing file size has been changed by another process
> - The file is on a network filesystem (NFS, CIFS, etc.)
> - The file is being modified concurrently

I don't think this make sense in real world. If a file is already used
by loop device, then user should avoid modifying this file directly. For
a file in fuse, I feel it's not good to use it as loop device.

Response---

>>I encountered this issue specifically with Lustre filesystem during testing
>> I did following --

>>1. File was created on Lustre

>>2. dd was done to write data on the file

>>3. ls confirmed the size

>>4. Loop device setup was done on the file immediately

>>5. write was issued with less space

>>6.above happened as file size was not correctly captured by loop device

>>I agree that network/distributed filesystems aren't ideal for loop devices,

>>but they are used in practice (container images on shared storage, diskless

>>systems, etc.). The fallback to i_size_read() ensures no performance penalty

>>for local filesystems while improving reliability for network filesystems.

____


> - The most accurate size is needed for loop device setup
> > The implementation gracefully falls back to i_size_read() if
vfs_getattr_nosec()
> fails, maintaining backward compatibility.

Response –

___

>>> you mean using the flag sync has backward compatibility issue ? or using function itself ?

___


>>
> Signed-off-by: Rajeev Mishra <rajeevm@hpe.com>
> ---
>   drivers/block/loop.c | 31 +++++++++++++++++++++++++++++--
>   1 file changed, 29 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 1b6ee91f8eb9..15d5edbc69ce 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -137,12 +137,39 @@ static void loop_global_unlock(struct loop_device *lo, bool global)
>   static int max_part;
>   static int part_shift;
>  
> +/**
> + * get_size - calculate the effective size of a loop device
> + * @offset: offset into the backing file
> + * @sizelimit: user-specified size limit
> + * @file: the backing file
> + *
> + * Calculate the effective size of the loop device
> + *
> + * Returns: size in 512-byte sectors, or 0 if invalid
> + */
>   static loff_t get_size(loff_t offset, loff_t sizelimit, struct file *file)
>   {
> +     struct kstat stat;
>        loff_t loopsize;
> +     int ret;
> +
> +     /*
> +      * Get file attributes for validation. We use vfs_getattr() to ensure
> +      * we have up-to-date file size information.
> +      */
> +     ret = vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE,
> +                             AT_STATX_SYNC_AS_STAT);
> +     if (ret) {
> +             /*
> +              * If we can't get attributes, fall back to i_size_read()
> +              * which should work for most cases.
> +              */
> +             loopsize = i_size_read(file->f_mapping->host);
> +     } else {
> +             /* Use the size from getattr for consistency */
> +             loopsize = stat.size;
> +     }

I'm ok switch from i_size_read() to getattr, however, the commit message
is confusing for me :(


Response --
>> I will make the commit message clear and simple. Just wanted to understand

>> if using this will be good “vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE, 0);”

>> is good I will replace i_size_read() with above code

>> do let me know if this will have any backward compatibility issue

>>Thanks again for your help

 


Thanks,
Kuai
>  
> -     /* Compute loopsize in bytes */
> -     loopsize = i_size_read(file->f_mapping->host);
>        if (offset > 0)
>                loopsize -= offset;
>        /* offset is beyond i_size, weird but possible */
>