Re: [PATCH 1/1] [RFC] 64bit copy_file_range system call

[Anna Schumaker <schumaker.anna@gmail.com>]

On 06/24/2017 09:23 AM, Jeff Layton wrote:
> On Wed, 2017-06-14 at 13:06 -0400, Olga Kornievskaia wrote:
>> This is a proposal to allow 64bit count to copy and return as
>> a result of a copy_file_range. No attempt was made to share code
>> with the 32bit function because 32bit interface should probably
>> get depreciated.
>>
>> Why use 64bit? Current uses of 32bit are by clone_file_range()
>> which could use 64bit count and NFS copy_file_range also supports
>> 64bit count value.
>>
>> Also with this proposal off-the-bet allow the userland to copy
>> between different mount points.
>>
>> Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
>> ---
>>  arch/x86/entry/syscalls/syscall_32.tbl |   1 +
>>  arch/x86/entry/syscalls/syscall_64.tbl |   1 +
>>  fs/read_write.c                        | 136 +++++++++++++++++++++++++++++++++
>>  include/linux/fs.h                     |   4 +
>>  include/linux/syscalls.h               |   3 +
>>  include/uapi/asm-generic/unistd.h      |   4 +-
>>  kernel/sys_ni.c                        |   1 +
>>  7 files changed, 149 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
>> index 448ac21..1f5f1e7 100644
>> --- a/arch/x86/entry/syscalls/syscall_32.tbl
>> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
>> @@ -391,3 +391,4 @@
>>  382	i386	pkey_free		sys_pkey_free
>>  383	i386	statx			sys_statx
>>  384	i386	arch_prctl		sys_arch_prctl			compat_sys_arch_prctl
>> +385	i386	copy_file_range64	sys_copy_file_range64
>> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
>> index 5aef183..e658bbe 100644
>> --- a/arch/x86/entry/syscalls/syscall_64.tbl
>> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
>> @@ -339,6 +339,7 @@
>>  330	common	pkey_alloc		sys_pkey_alloc
>>  331	common	pkey_free		sys_pkey_free
>>  332	common	statx			sys_statx
>> +333	64	copy_file_range64	sys_copy_file_range64
>>  
>>  #
>>  # x32-specific system call numbers start at 512 to avoid cache impact
>> diff --git a/fs/read_write.c b/fs/read_write.c
>> index 47c1d44..e2665c1 100644
>> --- a/fs/read_write.c
>> +++ b/fs/read_write.c
>> @@ -1700,6 +1700,142 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
>>  	return ret;
>>  }
>>  
>> +u64 vfs_copy_file_range64(struct file *file_in, loff_t pos_in,
>> +			    struct file *file_out, loff_t pos_out,
>> +			    u64 len, unsigned int flags)
>> +{
>> +	struct inode *inode_in = file_inode(file_in);
>> +	struct inode *inode_out = file_inode(file_out);
>> +	u64 ret;
>> +
>> +	if (flags != 0)
>> +		return -EINVAL;
>> +
>> +	if (S_ISDIR(inode_in->i_mode) || S_ISDIR(inode_out->i_mode))
>> +		return -EISDIR;
>> +	if (!S_ISREG(inode_in->i_mode) || !S_ISREG(inode_out->i_mode))
>> +		return -EINVAL;
>> +
>> +	ret = rw_verify_area(READ, file_in, &pos_in, len);
>> +	if (unlikely(ret))
>> +		return ret;
>> +
>> +	ret = rw_verify_area(WRITE, file_out, &pos_out, len);
>> +	if (unlikely(ret))
>> +		return ret;
>> +
>> +	if (!(file_in->f_mode & FMODE_READ) ||
>> +	    !(file_out->f_mode & FMODE_WRITE) ||
>> +	    (file_out->f_flags & O_APPEND))
>> +		return -EBADF;
>> +
>> +	if (len == 0)
>> +		return 0;
>> +
>> +	file_start_write(file_out);
>> +
>> +	/*
>> +	 * Try cloning first, this is supported by more file systems, and
>> +	 * more efficient if both clone and copy are supported (e.g. NFS).
>> +	 */
>> +	if (file_in->f_op->clone_file_range) {
>> +		ret = file_in->f_op->clone_file_range(file_in, pos_in,
>> +				file_out, pos_out, len);
>> +		if (ret == 0) {
>> +			ret = len;
>> +			goto done;
>> +		}
>> +	}
>> +
>> +	if (file_out->f_op->copy_file_range64) {
>> +		ret = file_out->f_op->copy_file_range64(file_in, pos_in,
>> +					file_out, pos_out, len, flags);
>> +		if (ret != -EOPNOTSUPP)
>> +			goto done;
>> +	}
>> +
>> +	ret = do_splice_direct(file_in, &pos_in, file_out, &pos_out,
>> +			len > MAX_RW_COUNT ? MAX_RW_COUNT : len, 0);
>> +
>> +done:
>> +	if (ret > 0) {
>> +		fsnotify_access(file_in);
>> +		add_rchar(current, ret);
>> +		fsnotify_modify(file_out);
>> +		add_wchar(current, ret);
>> +	}
>> +
>> +	inc_syscr(current);
>> +	inc_syscw(current);
>> +
>> +	file_end_write(file_out);
>> +
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL(vfs_copy_file_range64);
>> +
>> +SYSCALL_DEFINE6(copy_file_range64, int, fd_in, loff_t __user *, off_in,
>> +		int, fd_out, loff_t __user *, off_out,
>> +		u64, len, unsigned int, flags)
>> +{
>> +	loff_t pos_in;
>> +	loff_t pos_out;
>> +	struct fd f_in;
>> +	struct fd f_out;
>> +	u64 ret = -EBADF;
>> +
>> +	f_in = fdget(fd_in);
>> +	if (!f_in.file)
>> +		goto out2;
>> +
>> +	f_out = fdget(fd_out);
>> +	if (!f_out.file)
>> +		goto out1;
>> +
>> +	ret = -EFAULT;
>> +	if (off_in) {
>> +		if (copy_from_user(&pos_in, off_in, sizeof(loff_t)))
>> +			goto out;
>> +	} else {
>> +		pos_in = f_in.file->f_pos;
>> +	}
>> +
>> +	if (off_out) {
>> +		if (copy_from_user(&pos_out, off_out, sizeof(loff_t)))
>> +			goto out;
>> +	} else {
>> +		pos_out = f_out.file->f_pos;
>> +	}
>> +
>> +	ret = vfs_copy_file_range64(f_in.file, pos_in, f_out.file, pos_out, len,
>> +				  flags);
>> +	if (ret > 0) {
>> +		pos_in += ret;
>> +		pos_out += ret;
>> +
>> +		if (off_in) {
>> +			if (copy_to_user(off_in, &pos_in, sizeof(loff_t)))
>> +				ret = -EFAULT;
>> +		} else {
>> +			f_in.file->f_pos = pos_in;
>> +		}
>> +
>> +		if (off_out) {
>> +			if (copy_to_user(off_out, &pos_out, sizeof(loff_t)))
>> +				ret = -EFAULT;
>> +		} else {
>> +			f_out.file->f_pos = pos_out;
>> +		}
>> +	}
>> +
>> +out:
>> +	fdput(f_out);
>> +out1:
>> +	fdput(f_in);
>> +out2:
>> +	return ret;
>> +}
>> +
>>  static int clone_verify_area(struct file *file, loff_t pos, u64 len, bool write)
>>  {
>>  	struct inode *inode = file_inode(file);
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index 803e5a9..2727a98 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -1690,6 +1690,8 @@ struct file_operations {
>>  			u64);
>>  	ssize_t (*dedupe_file_range)(struct file *, u64, u64, struct file *,
>>  			u64);
>> +	u64 (*copy_file_range64)(struct file *, loff_t, struct file *,
>> +			loff_t, u64, unsigned int);
>>  };
>>  
>>  struct inode_operations {
>> @@ -1770,6 +1772,8 @@ extern int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
>>  					 loff_t len, bool *is_same);
>>  extern int vfs_dedupe_file_range(struct file *file,
>>  				 struct file_dedupe_range *same);
>> +extern u64 vfs_copy_file_range64(struct file *, loff_t, struct file *,
>> +			       loff_t, u64, unsigned int);
>>  
>>  struct super_operations {
>>     	struct inode *(*alloc_inode)(struct super_block *sb);
>> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
>> index 980c3c9..f7ea78e 100644
>> --- a/include/linux/syscalls.h
>> +++ b/include/linux/syscalls.h
>> @@ -905,5 +905,8 @@ asmlinkage long sys_pkey_mprotect(unsigned long start, size_t len,
>>  asmlinkage long sys_pkey_free(int pkey);
>>  asmlinkage long sys_statx(int dfd, const char __user *path, unsigned flags,
>>  			  unsigned mask, struct statx __user *buffer);
>> +asmlinkage long sys_copy_file_range64(int fd_in, loff_t __user *off_in,
>> +				    int fd_out, loff_t __user *off_out,
>> +				    u64 len, unsigned int flags);
>>  
>>  #endif
>> diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
>> index 061185a..e385a76 100644
>> --- a/include/uapi/asm-generic/unistd.h
>> +++ b/include/uapi/asm-generic/unistd.h
>> @@ -731,9 +731,11 @@
>>  __SYSCALL(__NR_pkey_free,     sys_pkey_free)
>>  #define __NR_statx 291
>>  __SYSCALL(__NR_statx,     sys_statx)
>> +#define __NR_copy_file_range64 292
>> +__SYSCALL(__NR_copy_file_range64, sys_copy_file_range64)
>>  
>>  #undef __NR_syscalls
>> -#define __NR_syscalls 292
>> +#define __NR_syscalls 293
>>  
>>  /*
>>   * All syscalls below here should go away really,
>> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
>> index 8acef85..8e0cfd4 100644
>> --- a/kernel/sys_ni.c
>> +++ b/kernel/sys_ni.c
>> @@ -178,6 +178,7 @@ asmlinkage long sys_ni_syscall(void)
>>  cond_syscall(sys_capget);
>>  cond_syscall(sys_capset);
>>  cond_syscall(sys_copy_file_range);
>> +cond_syscall(sys_copy_file_range64);
>>  
>>  /* arch-specific weak syscall entries */
>>  cond_syscall(sys_pciconfig_read);
> 
> Hi Olga,
> 
> We discussed this a bit privately, but I'll note it here too.
> 
> Server-to-server copy seems like a nice thing to me as well. There are
> several filesystems that can likely make use of that ability.
> 
> I don't have a real opinion on the API change either, but you're making
> a very subtle change with this patch. Prior to this, the existing
> copy_file_range calls could count on the superblocks being the same.
> Now, it looks like you can pass them any old file pointer.

What if we add a new file op for xdev copy that gets called when superblocks are different, but filesystem type is the same?  We could keep the current copy_file_range fop to fall back on if superblocks are the same.

Thoughts?
Anna

> 
> The exsiting copy_file_range file ops need to be fixed to vet the struct
> files they've been handed if you want to do this.
> 
> It would also be nice to see something on copy_file_range and
> clone_file_range in Documentation/filesystems/vfs.txt.
> 
> Cheers,
>