On Thu, 3 Jun 2010 21:44:06 +0530, "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> wrote: > 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 > > Changes from V12: > a) Use CAP_DAC_READ_SEARCH instead of CAP_DAC_OVERRIDE in open_by_handle > b) Return -ENOTDIR if O_DIRECTORY flag is specified in open_by_handle with > handle for non directory > > Changes from V11: > a) Add necessary documentation to different functions > b) Add null pathname support to faccessat and linkat similar to > readlinkat. > c) compile fix on x86_64 > > Changes from V10: > a) Missed an stg refresh before sending out the patchset. Send > updated patchset. > > Changes from V9: > a) Fix compile errors with CONFIG_EXPORTFS not defined > b) Return -EOPNOTSUPP if file system doesn't support fh_to_dentry exportfs callback. > > Changes from V8: > a) exportfs_decode_fh now returns -ESTALE if export operations is not defined. > b) drop get_fsid super_operations. Instead use superblock to store uuid. > > Changes from V7: > a) open_by_handle now use mountdirfd to identify the vfsmount. > b) We don't validate the UUID passed as a part of file handle in open_by_handle. > UUID is provided as a part of file handle as an easy way for userspace to > use the kernel returned handle as it is. It also helps in finding the 16 byte > filessytem UUID in userspace without using file system specific libraries to > read file system superblock. If a particular file system doesn't support UUID > or any form of unique id this field in the file handle will be zero filled. > c) drop freadlink syscall. Instead use readlinkat with NULL pathname to indicate > read the link target name of the link pointed by fd. This is similar to > sys_utimensat > d) Instead of opencoding all the open flag related check use helper functions. > Did finish_open_by_handle similar to finish_open. > c) Fix may_open to not return ELOOP for symlink when we are called from handle open. > open(2) still returns error as expected. > > 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) > ------- > cc <source.c> -luuid > -------- > #define _GNU_SOURCE > #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> > #include <uuid/uuid.h> > > struct file_handle { > int handle_size; > int handle_type; > uuid_t fs_uuid; > unsigned char handle[0]; > }; > > #define AT_FDCWD -100 > #define AT_SYMLINK_FOLLOW 0x400 > > static int name_to_handle(const char *name, struct file_handle *fh) > { > return syscall(338, AT_FDCWD, name, fh, AT_SYMLINK_FOLLOW); > } > > static int lname_to_handle(const char *name, struct file_handle *fh) > { > return syscall(338, AT_FDCWD, name, fh, 0); > } > > static int open_by_handle(int mountfd, struct file_handle *fh, int flags) > { > return syscall(339, mountfd, fh, flags); > } > > #define BUFSZ 100 > int main(int argc, char *argv[]) > { > int fd; > int ret; > int mountfd; > int handle_sz; > struct stat bufstat; > char buf[BUFSZ]; > char uuid[36]; > struct file_handle *fh = NULL;; > if (argc != 3 ) { > printf("Usage: %s <filename> <mount-dir-name>\n", argv[0]); > exit(1); > } > 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) { > printf("Found the handle size needed to be %d\n", fh->handle_size); > goto again; > } else if (ret) { > perror("Error:"); > exit(1); > } > uuid_unparse(fh->fs_uuid, uuid); > printf("UUID:%s\n", uuid); > printf("Waiting for input"); > getchar(); > mountfd = open(argv[2], O_RDONLY | O_DIRECTORY); > if (mountfd <= 0) { > perror("Error:"); > exit(1); > } > fd = open_by_handle(mountfd, fh, O_RDONLY); > if (fd <= 0 ) { > perror("Error:"); > exit(1); > } > printf("Reading the content now \n"); > fstat(fd, &bufstat); > ret = S_ISLNK(bufstat.st_mode); > if (ret) { > memset(buf, 0 , BUFSZ); > readlinkat(fd, NULL, 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); > } > /* Now check for faccess */ > if (faccessat(fd, NULL, W_OK, 0) == 0) { > printf("Got write permission on the file \n"); > } else > perror("faccess error"); > /* now try to create a hardlink */ > if (linkat(fd, NULL, AT_FDCWD, "test", 0) == 0){ > printf("created hardlink\n"); > } else > perror("linkat error"); > return 0; > } > > git tree for this patch series is available at http://git.kernel.org/?p=linux/kernel/git/kvaneesh/linux-open-handle.git git://git.kernel.org/pub/scm/linux/kernel/git/kvaneesh/linux-open-handle.git open-by-handle-v13 -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
