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* [PATCH -V7 0/8] Generic name to handle and open by handle syscalls
@ 2010-05-12 15:50 Aneesh Kumar K.V
  2010-05-12 15:50 ` [PATCH -V7 1/9] exportfs: Return the minimum required handle size Aneesh Kumar K.V
                   ` (8 more replies)
  0 siblings, 9 replies; 47+ messages in thread
From: Aneesh Kumar K.V @ 2010-05-12 15:50 UTC (permalink / raw)
  To: hch, viro, adilger, corbet, serue, neilb
  Cc: linux-fsdevel, sfrench, philippe.deniel, linux-kernel

Hi,

The below set of patches implement open by handle support using exportfs
operations. This allows user space application to map a file name to file 
handle and later open the file using handle. This should be usable
for userspace NFS [1] and 9P server [2]. XFS already support this with the ioctls
XFS_IOC_PATH_TO_HANDLE and XFS_IOC_OPEN_BY_HANDLE.

[1] http://nfs-ganesha.sourceforge.net/
[2] http://thread.gmane.org/gmane.comp.emulators.qemu/68992

I guess v7 address all the review comments. If I have missing some please let me
know. I am also looking at getting xfsprogs libhandle.so on top of these syscalls.
Let me know if you have any objection towards merging this patchset upstream.

Changes from V6:
a) Add uuid to vfsmount lookup and drop uuid to superblock lookup
b) Return -EOPNOTSUPP in sys_name_to_handle if the file system returned uuid
   doesn't give the same vfsmount on lookup. This ensure that we fail
   sys_name_to_handle when we have multiple file system returning same UUID.

Changes from V5:
a) added sys_name_to_handle_at syscall which takes AT_SYMLINK_NOFOLLOW flag 
   instead of two syscalls sys_name_to_handle and sys_lname_to_handle.
b) addressed review comments from Niel Brown
c) rebased to b91ce4d14a21fc04d165be30319541e0f9204f15
d) Add compat_sys_open_by_handle

Chages from V4:
a) Changed the syscal arguments so that we don't need compat syscalls
   as suggested by Christoph
c) Added two new syscall sys_lname_to_handle and sys_freadlink to work with
   symlinks
d) Changed open_by_handle to work with all file types
e) Add ext3 support

Changes from V3:
a) Code cleanup suggested by Andreas
b) x86_64 syscall support
c) add compat syscall

Chages from V2:
a) Support system wide unique handle.

Changes from v1:
a) handle size is now specified in bytes
b) returns -EOVERFLOW if the handle size is small
c) dropped open_handle syscall and added open_by_handle_at syscall
   open_by_handle_at takes mount_fd as the directory fd of the mount point
   containing the file
e) handle will only be unique in a given file system. So for an NFS server
   exporting multiple file system, NFS server will have to internally track the
   mount point to which a file handle belongs to. We should be able to do it much
   easily than expecting kernel to give a system wide unique file handle. System
   wide unique file handle would need much larger changes to the exportfs or VFS
   interface and I was not sure whether we really need to do that in the kernel or
   in the user space
f) open_handle_at now only check for DAC_OVERRIDE capability


Example program: (x86_32). (x86_64 would need a different syscall number)
----------------
#include <stdio.h>
#include <stdlib.h>

#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>

struct uuid {
	unsigned char uuid[16];
};
struct file_handle {
        int handle_size;
        int handle_type;
	struct uuid fsid;
        unsigned char handle[0];
};


#define AT_FDCWD		-100
#define AT_SYMLINK_NOFOLLOW	0x100

static int name_to_handle(const char *name, struct file_handle  *fh)
{
	return syscall(338, AT_FDCWD, name, fh, 0);
}

static int lname_to_handle(const char *name, struct file_handle  *fh)
{
	return syscall(338, AT_FDCWD, name, fh, AT_SYMLINK_NOFOLLOW);
}

static int open_by_handle(struct file_handle *fh,  int flags)
{
	return syscall(339, fh, flags);
}

static int freadlink(int fd, char *buf, size_t bufsiz)
{
	return syscall(340, fd, buf, bufsiz);
}

#define BUFSZ 100
int main(int argc, char *argv[])
{
        int ret;
	int handle_sz;
	struct stat bufstat;
        int fd, dirfd;
        char buf[BUFSZ];
        struct file_handle *fh = NULL;;
again:
	if (fh && fh->handle_size) {
		handle_sz = fh->handle_size;
		free(fh);
		fh = malloc(sizeof(struct file_handle) + handle_sz);
		fh->handle_size = handle_sz;
	} else {
		fh = malloc(sizeof(struct file_handle));
		fh->handle_size = 0;
	}
        errno  = 0;
        ret = lname_to_handle(argv[1], fh);
        if (ret && errno == EOVERFLOW) {
                perror("Error:");
		printf("Found the handle size needed to be %d\n", fh->handle_size);
		printf("Trying again..\n");
		goto again;
        } else if (ret) {
                perror("Error:");
		exit(1);
	}
        fd = open_by_handle(fh, O_RDONLY);
        if (fd <= 0 ) {
                perror("Error:");
                exit(1);
        }
	fstat(fd, &bufstat);
	ret = S_ISLNK(bufstat.st_mode);
	if (ret) {
	        memset(buf, 0 , BUFSZ);
		freadlink(fd, buf, BUFSZ);
		printf("%s is a symlink pointing to %s\n", argv[1], buf);
	}
        memset(buf, 0 , BUFSZ);
	while (1) {
		ret = read(fd, buf, BUFSZ -1);
		if (ret <= 0)
			break;
		buf[ret] = '\0';
                printf("%s", buf);
                memset(buf, 0 , BUFSZ);
        }
        return 0;
}

-aneesh

^ permalink raw reply	[flat|nested] 47+ messages in thread
end of thread, other threads:[~2010-05-15 15:28 UTC | newest]

Thread overview: 47+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2010-05-12 15:50 [PATCH -V7 0/8] Generic name to handle and open by handle syscalls Aneesh Kumar K.V
2010-05-12 15:50 ` [PATCH -V7 1/9] exportfs: Return the minimum required handle size Aneesh Kumar K.V
2010-05-12 15:50 ` [PATCH -V7 2/9] vfs: Add uuid based vfsmount lookup Aneesh Kumar K.V
2010-05-12 15:50 ` [PATCH -V7 3/9] vfs: Add name to file handle conversion support Aneesh Kumar K.V
2010-05-12 21:49   ` Andreas Dilger
2010-05-12 22:43     ` Neil Brown
2010-05-13  6:17       ` Aneesh Kumar K. V
2010-05-13  7:11         ` Neil Brown
2010-05-13  8:30           ` Andreas Dilger
2010-05-13  8:47             ` Neil Brown
2010-05-13 14:21             ` Aneesh Kumar K. V
2010-05-13 18:17               ` Aneesh Kumar K. V
2010-05-13 22:54                 ` Andreas Dilger
2010-05-14 17:25                   ` Al Viro
2010-05-14 18:18                     ` Aneesh Kumar K. V
2010-05-14 18:40                       ` Al Viro
2010-05-15  5:31                         ` Aneesh Kumar K. V
2010-05-15  6:00                           ` Al Viro
2010-05-15 15:28                             ` Aneesh Kumar K. V
2010-05-13  0:20     ` Dave Chinner
2010-05-13  6:23       ` Aneesh Kumar K. V
2010-05-13  7:31         ` Dave Chinner
2010-05-13  5:56     ` Aneesh Kumar K. V
2010-05-13 14:24     ` Aneesh Kumar K. V
2010-05-12 15:50 ` [PATCH -V7 4/9] vfs: Add open by file handle support Aneesh Kumar K.V
2010-05-12 23:44   ` Neil Brown
2010-05-13  6:09     ` Dave Chinner
2010-05-13  6:37       ` Aneesh Kumar K. V
2010-05-14 10:41         ` Dave Chinner
2010-05-12 15:50 ` [PATCH -V7 5/9] vfs: Add freadlink syscall Aneesh Kumar K.V
2010-05-13  1:43   ` Neil Brown
2010-05-13  6:25     ` Aneesh Kumar K. V
2010-05-13  6:56       ` Neil Brown
2010-05-13  7:34         ` Aneesh Kumar K. V
2010-05-13  8:09           ` Neil Brown
2010-05-14 11:18         ` Aneesh Kumar K. V
2010-05-12 15:50 ` [PATCH -V7 6/9] ext4: Add get_fsid callback Aneesh Kumar K.V
2010-05-13  3:11   ` Dave Chinner
2010-05-13  6:32     ` Aneesh Kumar K. V
2010-05-14  1:44       ` Dave Chinner
2010-05-15  6:09         ` Aneesh Kumar K. V
2010-05-14 17:32   ` Coly Li
2010-05-14 18:21     ` Aneesh Kumar K. V
2010-05-14 19:08       ` Coly Li
2010-05-12 15:50 ` [PATCH -V7 7/9] x86: Add new syscalls for x86_32 Aneesh Kumar K.V
2010-05-12 15:50 ` [PATCH -V7 8/9] x86: Add new syscalls for x86_64 Aneesh Kumar K.V
2010-05-12 15:50 ` [PATCH -V7 9/9] ext3: Add get_fsid callback Aneesh Kumar K.V

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