Hi,
Attached is a patch against 2.4.0-test5 which implements
flink(fd, newname)
It allows you to link a file with inode->nlink == 0 back into the
filesystem, so it won't be garbage-collected when your process exits.
% echo 'Hello, world!' > old
% ll -i
total 0
32619 -rw-r--r-- 1 remi users 14 Jul 31 15:44 old
% exec 5<old
% rm old
% ll -i
total 0
% ~/src/flink/flink 5 new
% ll -i
total 0
32619 -rw-r--r-- 1 remi users 14 Jul 31 15:44 new
% cat new
Hello, world!
%
My second idea is related and even crazier:
Temporary files are often create(2)ed and then unlink(2)ed.
create(2) creates an inode and a hard-link. You then use unlink(2)
to remove the hard-link.
So I've been thinking about an O_ANONYMOUS or O_NONAME flag for open(2)
to specify you don't want any name for it.
(So create(2) with O_ANONYMOUS + flink(2) would be the same (except
non-atomic) as create(2))
However, the ->create method of struct inode_operations already creates
the first name for the file. Which brings me to my next idea:
What if ->create only creates the inode, not the first hard-link?
If the O_ANONYMOUS flag is not given, the VFS could then call the ->link
method for the creation of the first hardlink.
(I'm afraid this would cause trouble for filesystems without support
for nlink > 1 like FAT.)
P.S. flink(2) is my first patch, so please don't laugh too hard ;-).
-- Linux localhost.localdomain 2.4.0-test5 #1 Mon Jul 31 13:21:59 CEST 2000
#include <linux/unistd.h> #include <stdlib.h> #include <stdio.h>
_syscall2(long, flink, unsigned int, fd, const char *, newname)
int main(int argc, char **argv) { if (argc != 3) { fprintf(stderr, "Usage: flink fd newname\n"); return 1; } if (flink(atoi(argv[1]), argv[2]) < 0) { perror("flink"); return 1; } return 0; }
diff -urN linux-2.4.0-test5-std/arch/i386/kernel/entry.S linux-2.4.0-test5-flink/arch/i386/kernel/entry.S --- linux-2.4.0-test5-std/arch/i386/kernel/entry.S Sun Jul 30 12:48:23 2000 +++ linux-2.4.0-test5-flink/arch/i386/kernel/entry.S Mon Jul 31 13:22:35 2000 @@ -641,6 +641,7 @@ .long SYMBOL_NAME(sys_pivot_root) .long SYMBOL_NAME(sys_mincore) .long SYMBOL_NAME(sys_madvise) + .long SYMBOL_NAME(sys_flink) /* @@ -649,6 +650,6 @@ * entries. Don't panic if you notice that this hasn't * been shrunk every time we add a new system call. */ - .rept NR_syscalls-219 + .rept NR_syscalls-220 .long SYMBOL_NAME(sys_ni_syscall) .endr diff -urN linux-2.4.0-test5-std/fs/namei.c linux-2.4.0-test5-flink/fs/namei.c --- linux-2.4.0-test5-std/fs/namei.c Sun Jul 30 12:48:40 2000 +++ linux-2.4.0-test5-flink/fs/namei.c Mon Jul 31 21:54:09 2000 @@ -21,6 +21,7 @@ #include <linux/quotaops.h> #include <linux/pagemap.h> #include <linux/dcache.h> +#include <linux/file.h> #include <asm/uaccess.h> #include <asm/unaligned.h> @@ -1598,6 +1599,62 @@ } putname(from); + return error; +} + +asmlinkage long sys_flink(unsigned int fd, const char *newname) +{ + int error; + struct file *file; + struct dentry *dentry; + const char *to; + + error = -EBADF; + file = fget(fd); + if (!file) + goto exit; + + to = getname(newname); + error = PTR_ERR(to); + if (!IS_ERR(to)) { + + struct dentry *new_dentry; + struct nameidata nd; + + error = 0; + + dentry = file->f_dentry; + + /* Where (and why) should I put this (un)lock_kernel() */ + lock_kernel(); + + if (path_init(to, LOOKUP_PARENT, &nd)) + error = path_walk(to, &nd); + if (error) + goto out; + + error = -EXDEV; + if (file->f_vfsmnt != nd.mnt) + goto out; + + new_dentry = lookup_create(&nd, 0); + error = PTR_ERR(new_dentry); + if (!IS_ERR(new_dentry)) { + error = vfs_link(dentry, nd.dentry->d_inode, new_dentry); + /* Where is the corresponding dget? */ + dput(new_dentry); + } + + /* lookup_create() down()s it */ + up(&nd.dentry->d_inode->i_sem); + + path_release(&nd); + } +out: + unlock_kernel(); + putname(to); + fput(file); +exit: return error; } diff -urN linux-2.4.0-test5-std/include/asm-i386/unistd.h linux-2.4.0-test5-flink/include/asm-i386/unistd.h --- linux-2.4.0-test5-std/include/asm-i386/unistd.h Sun Apr 30 19:13:12 2000 +++ linux-2.4.0-test5-flink/include/asm-i386/unistd.h Mon Jul 31 13:22:35 2000 @@ -225,6 +225,7 @@ #define __NR_mincore 218 #define __NR_madvise 219 #define __NR_madvise1 219 /* delete when C lib stub is removed */ +#define __NR_flink 220 /* user-visible error numbers are in the range -1 - -124: see <asm-i386/errno.h> */
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This archive was generated by hypermail 2b29 : Mon Jul 31 2000 - 21:00:34 EST