Copy system calls came up during Plumbers a while ago, mostly because several
filesystems (including NFS and XFS) are currently working on copy acceleration
implementations. We haven't heard from Zach Brown in a while, so I volunteered
to push his patches upstream so individual filesystems don't need to keep
writing their own ioctls.
The question has come up about how vfs_copy_file_range() responds to signals,
and I don't have a good answer. The pagecache copy option uses splice,
which (as far as I can tell) doesn't get interrupted. Please let me know if
I'm missing something or completely misunderstanding the question!
Changes in v3:
- Update against the most recent Linus kernel
- Flags parameter should be an unsigned int
- Add COPY_FR_DEDUPE flag for Darrick
- Make each flag exclusive
- Update man page
- Added "Reiewed-by" tags
I tested the COPY_FR_COPY flag by using /dev/urandom to generate files of
varying sizes and copying them. I compared the output from `time` against
that of `cp` to see if there is any noticable difference. Values in the
tables below are averages across multiple trials.
/usr/bin/cp | 512 | 1024 | 1536 | 2048 | 2560 | 3072 | 5120
-------------|--------|--------|--------|--------|--------|--------|--------
user | 0.00s | 0.00s | 0.01s | 0.01s | 0.01s | 0.01s | 0.02s
system | 0.92s | 0.59s | 0.88s | 1.18s | 1.48s | 1.78s | 2.98s
cpu | 43% | 18% | 17% | 18% | 18% | 18% | 17%
total | 2.116 | 3.200 | 4.950 | 6.541 | 8.105 | 9.811 | 17.211
VFS Copy | 512 | 1024 | 1536 | 2048 | 2560 | 3072 | 5120
-------------|--------|--------|--------|--------|--------|--------|--------
user | 0.00s | 0.00s | 0.00s | 0.00s | 0.00s | 0.00s | 0.00s
system | 0.80s | 0.56s | 0.84s | 1.10s | 1.39s | 1.67s | 2.81s
cpu | 41% | 18% | 19% | 17% | 17% | 17% | 17%
total | 1.922 | 2.990 | 4.448 | 6.292 | 7.855 | 9.480 | 15.944
Questions? Comments? Thoughts?
Anna
Anna Schumaker (6):
vfs: Copy should check len after file open mode
vfs: Copy shouldn't forbid ranges inside the same file
vfs: Copy should use file_out rather than file_in
vfs: Remove copy_file_range mountpoint checks
vfs: copy_file_range() can do a pagecache copy with splice
btrfs: btrfs_copy_file_range() only supports reflinks
Zach Brown (3):
vfs: add copy_file_range syscall and vfs helper
x86: add sys_copy_file_range to syscall tables
btrfs: add .copy_file_range file operation
arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
fs/btrfs/ctree.h | 3 +
fs/btrfs/file.c | 1 +
fs/btrfs/ioctl.c | 95 +++++++++++++---------
fs/read_write.c | 141 +++++++++++++++++++++++++++++++++
include/linux/copy.h | 6 ++
include/linux/fs.h | 3 +
include/uapi/asm-generic/unistd.h | 2 +
include/uapi/linux/Kbuild | 1 +
include/uapi/linux/copy.h | 8 ++
kernel/sys_ni.c | 1 +
12 files changed, 224 insertions(+), 39 deletions(-)
create mode 100644 include/linux/copy.h
create mode 100644 include/uapi/linux/copy.h
--
2.5.3
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