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loop: sync filesystem cache before getting file size in get_size() #96

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loop: sync filesystem cache before getting file size in get_size() #96

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31 changes: 29 additions & 2 deletions drivers/block/loop.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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 */
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