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Subject[PATCH 03/45] fs: add ksys_lseek() helper; remove in-kernel calls to sys_lseek()
Date
Using this helper allows us to avoid the in-kernel calls to the
sys_lseek() syscall. The ksys_ prefix denotes that this function
is meant as a drop-in replacement for the syscall. In particular, it
uses the same calling convention as sys_lseek().

This patch is part of a series which tries to remove in-kernel calls to
syscalls. On this basis, the syscall entry path can be streamlined.

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
---
fs/read_write.c | 9 +++++++--
include/linux/syscalls.h | 1 +
init/do_mounts_rd.c | 8 ++++----
3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 8e8f0b4f52e2..b38b008a078e 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -301,7 +301,7 @@ loff_t vfs_llseek(struct file *file, loff_t offset, int whence)
}
EXPORT_SYMBOL(vfs_llseek);

-SYSCALL_DEFINE3(lseek, unsigned int, fd, off_t, offset, unsigned int, whence)
+off_t ksys_lseek(unsigned int fd, off_t offset, unsigned int whence)
{
off_t retval;
struct fd f = fdget_pos(fd);
@@ -319,10 +319,15 @@ SYSCALL_DEFINE3(lseek, unsigned int, fd, off_t, offset, unsigned int, whence)
return retval;
}

+SYSCALL_DEFINE3(lseek, unsigned int, fd, off_t, offset, unsigned int, whence)
+{
+ return ksys_lseek(fd, offset, whence);
+}
+
#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE3(lseek, unsigned int, fd, compat_off_t, offset, unsigned int, whence)
{
- return sys_lseek(fd, offset, whence);
+ return ksys_lseek(fd, offset, whence);
}
#endif

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index f1d341d0972f..d11d06ab546e 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -975,6 +975,7 @@ int ksys_fchown(unsigned int fd, uid_t user, gid_t group);
int ksys_getdents64(unsigned int fd, struct linux_dirent64 __user *dirent,
unsigned int count);
int ksys_ioctl(unsigned int fd, unsigned int cmd, unsigned long arg);
+off_t ksys_lseek(unsigned int fd, off_t offset, unsigned int whence);

/*
* The following kernel syscall equivalents are just wrappers to fs-internal
diff --git a/init/do_mounts_rd.c b/init/do_mounts_rd.c
index 4dafaed5736f..13e54148c0e0 100644
--- a/init/do_mounts_rd.c
+++ b/init/do_mounts_rd.c
@@ -90,7 +90,7 @@ identify_ramdisk_image(int fd, int start_block, decompress_fn *decompressor)
/*
* Read block 0 to test for compressed kernel
*/
- sys_lseek(fd, start_block * BLOCK_SIZE, 0);
+ ksys_lseek(fd, start_block * BLOCK_SIZE, 0);
sys_read(fd, buf, size);

*decompressor = decompress_method(buf, size, &compress_name);
@@ -136,7 +136,7 @@ identify_ramdisk_image(int fd, int start_block, decompress_fn *decompressor)
/*
* Read 512 bytes further to check if cramfs is padded
*/
- sys_lseek(fd, start_block * BLOCK_SIZE + 0x200, 0);
+ ksys_lseek(fd, start_block * BLOCK_SIZE + 0x200, 0);
sys_read(fd, buf, size);

if (cramfsb->magic == CRAMFS_MAGIC) {
@@ -150,7 +150,7 @@ identify_ramdisk_image(int fd, int start_block, decompress_fn *decompressor)
/*
* Read block 1 to test for minix and ext2 superblock
*/
- sys_lseek(fd, (start_block+1) * BLOCK_SIZE, 0);
+ ksys_lseek(fd, (start_block+1) * BLOCK_SIZE, 0);
sys_read(fd, buf, size);

/* Try minix */
@@ -178,7 +178,7 @@ identify_ramdisk_image(int fd, int start_block, decompress_fn *decompressor)
start_block);

done:
- sys_lseek(fd, start_block * BLOCK_SIZE, 0);
+ ksys_lseek(fd, start_block * BLOCK_SIZE, 0);
kfree(buf);
return nblocks;
}
--
2.16.2
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