```C
static inline void file_start_write(struct file *file)
{
if (!S_ISREG(file_inode(file)->i_mode))
return;
__sb_start_write(file_inode(file)->i_sb, SB_FREEZE_WRITE, true);
}

static inline bool file_start_write_trylock(struct file *file)
{
if (!S_ISREG(file_inode(file)->i_mode))
return true;
return __sb_start_write(file_inode(file)->i_sb, SB_FREEZE_WRITE, false);
}

static inline void file_end_write(struct file *file)
{
if (!S_ISREG(file_inode(file)->i_mode))
return;
__sb_end_write(file_inode(file)->i_sb, SB_FREEZE_WRITE);
}

ssize_t vfs_write(struct file *file, const char __user *buf, size_t count, loff_t *pos)
{
ssize_t ret;

if (!(file->f_mode & FMODE_WRITE))
return -EBADF;
if (!file->f_op || (!file->f_op->write && !file->f_op->aio_write))
return -EINVAL;
if (unlikely(!access_ok(VERIFY_READ, buf, count)))
return -EFAULT;

ret = rw_verify_area(WRITE, file, pos, count);
if (ret >= 0) {
count = ret;
file_start_write(file);
if (file->f_op->write)
ret = file->f_op->write(file, buf, count, pos);
else
ret = do_sync_write(file, buf, count, pos);
if (ret > 0) {
fsnotify_modify(file);
add_wchar(current, ret);
}
inc_syscw(current);
file_end_write(file);
}

return ret;
}
```