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fs: add ksys_lseek() helper; remove in-kernel calls to sys_lseek() 

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 removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
This commit is contained in:
Dominik Brodowski 2018-03-13 21:51:17 +01:00
parent cbb60b924b
commit 76847e4344
3 changed files with 12 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
fs/read_write.c
View File

@ -301,7 +301,7 @@ loff_t vfs_llseek(struct file *file, loff_t offset, int whence)
} }
EXPORT_SYMBOL(vfs_llseek); 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; off_t retval;
struct fd f = fdget_pos(fd); struct fd f = fdget_pos(fd);
@ -319,10 +319,15 @@ SYSCALL_DEFINE3(lseek, unsigned int, fd, off_t, offset, unsigned int, whence)
return retval; return retval;
} }
SYSCALL_DEFINE3(lseek, unsigned int, fd, off_t, offset, unsigned int, whence)
{
return ksys_lseek(fd, offset, whence);
}
#ifdef CONFIG_COMPAT #ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE3(lseek, unsigned int, fd, compat_off_t, offset, unsigned int, whence) 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 #endif

1
include/linux/syscalls.h
View File

@ -958,6 +958,7 @@ int ksys_fchown(unsigned int fd, uid_t user, gid_t group);
int ksys_getdents64(unsigned int fd, struct linux_dirent64 __user *dirent, int ksys_getdents64(unsigned int fd, struct linux_dirent64 __user *dirent,
unsigned int count); unsigned int count);
int ksys_ioctl(unsigned int fd, unsigned int cmd, unsigned long arg); 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 * The following kernel syscall equivalents are just wrappers to fs-internal

8
init/do_mounts_rd.c
View File

@ -90,7 +90,7 @@ identify_ramdisk_image(int fd, int start_block, decompress_fn *decompressor)
/* /*
* Read block 0 to test for compressed kernel * 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); sys_read(fd, buf, size);
*decompressor = decompress_method(buf, size, &compress_name); *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 * 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); sys_read(fd, buf, size);
if (cramfsb->magic == CRAMFS_MAGIC) { 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 * 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); sys_read(fd, buf, size);
/* Try minix */ /* Try minix */
@ -178,7 +178,7 @@ identify_ramdisk_image(int fd, int start_block, decompress_fn *decompressor)
start_block); start_block);
done: done:
sys_lseek(fd, start_block * BLOCK_SIZE, 0); ksys_lseek(fd, start_block * BLOCK_SIZE, 0);
kfree(buf); kfree(buf);
return nblocks; return nblocks;
} }