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* Re: [PATCH -V7 4/9] vfs: Add open by file handle support
@ 2010-05-14 19:56 Steve French
  2010-05-16  7:24 ` Aneesh Kumar K. V
  0 siblings, 1 reply; 7+ messages in thread
From: Steve French @ 2010-05-14 19:56 UTC (permalink / raw)
  To: linux-fsdevel, LKML

I think open by handle will turn out to be useful, but in discussing
various "duplicate inode number" checks that we are having to add to
cifs, it reminded me that we probably need a "generation number" or
some equivalent (birth time is probably good enough as well) to be
able to tell the case where a file is deleted and new file is created
reusing the same inode number (eventually Samba needs to return this
to posix clients if inode numbers are to be useful - and I don't know
how to tell Samba how to get birth time or generation numbers out of
stat in userspace)

-- 
Thanks,

Steve

^ permalink raw reply	[flat|nested] 7+ messages in thread
* [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 4/9] vfs: Add open by file handle support Aneesh Kumar K.V
  0 siblings, 1 reply; 7+ 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] 7+ messages in thread
end of thread, other threads:[~2010-05-16  7:24 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2010-05-14 19:56 [PATCH -V7 4/9] vfs: Add open by file handle support Steve French
2010-05-16  7:24 ` Aneesh Kumar K. V
  -- strict thread matches above, loose matches on Subject: below --
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 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

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