fs: add do_linkat() helper and ksys_link() wrapper; remove in-kernel calls to syscall
Using the fs-internal do_linkat() helper allows us to get rid of fs-internal calls to the sys_linkat() syscall. Introducing the ksys_link() wrapper allows us to avoid the in-kernel calls to sys_link() 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_link(). In the near future, the only fs-external user of ksys_link() should be converted to use vfs_link() instead. 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: Al Viro <viro@zeniv.linux.org.uk> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
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@ -62,6 +62,8 @@ long do_rmdir(int dfd, const char __user *pathname);
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long do_unlinkat(int dfd, struct filename *name);
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long do_symlinkat(const char __user *oldname, int newdfd,
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const char __user *newname);
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int do_linkat(int olddfd, const char __user *oldname, int newdfd,
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const char __user *newname, int flags);
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/*
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* namespace.c
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12
fs/namei.c
12
fs/namei.c
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@ -4250,8 +4250,8 @@ EXPORT_SYMBOL(vfs_link);
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* with linux 2.0, and to avoid hard-linking to directories
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* and other special files. --ADM
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*/
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SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
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int, newdfd, const char __user *, newname, int, flags)
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int do_linkat(int olddfd, const char __user *oldname, int newdfd,
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const char __user *newname, int flags)
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{
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struct dentry *new_dentry;
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struct path old_path, new_path;
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@ -4315,9 +4315,15 @@ out:
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return error;
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}
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SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
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int, newdfd, const char __user *, newname, int, flags)
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{
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return do_linkat(olddfd, oldname, newdfd, newname, flags);
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}
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SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname)
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{
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return sys_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
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return do_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
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}
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/**
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@ -997,4 +997,13 @@ static inline long ksys_mknod(const char __user *filename, umode_t mode,
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return do_mknodat(AT_FDCWD, filename, mode, dev);
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}
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extern int do_linkat(int olddfd, const char __user *oldname, int newdfd,
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const char __user *newname, int flags);
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static inline long ksys_link(const char __user *oldname,
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const char __user *newname)
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{
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return do_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
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}
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#endif
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@ -306,7 +306,7 @@ static int __init maybe_link(void)
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if (nlink >= 2) {
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char *old = find_link(major, minor, ino, mode, collected);
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if (old)
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return (sys_link(old, collected) < 0) ? -1 : 1;
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return (ksys_link(old, collected) < 0) ? -1 : 1;
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}
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return 0;
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}
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