ChorusOS man pages section 2POSIX: POSIX System Calls

mount(2POSIX)

NAME

mount, unmount- mount or unmount a filesystem

SYNOPSIS

#include <sys/param.h>
#include <sys/mount.h>

type

dir

flags

data

dir

flags

FEATURES

MSDOSFS, NFS_CLIENT, POSIX_SOCKETS, UFS

DESCRIPTION

The mount function grafts a filesystem object onto the system file tree at the point dir . The data argument describes the filesystem object to be mounted. The type argument defines how the kernel interprets data (See type below). The contents of the filesystem become available through the new mount point dir . Any files in dir at the time of a successful mount become hidden, and are unavailable until the filesystem is unmounted.

The following flags may be specified to suppress default semantics which affect filesystem access.

MNT_RDONLY: The filesystem should be treated as read-only; even the super-user may not write to it.
MNT_NOEXEC: Do not allow files to be executed from the filesystem.
MNT_NOSUID: Do not honor setuid or setgid bits on files when executing them.
MNT_NODEV: Do not interpret special files on the filesystem.
MNT_SYNCHRONOUS: All I/O to the filesystem should be done synchronously.
MNT_NOATIME: Disable update of file access times.
MNT_ASYNC: All I/O to the filesystem should be done asynchronously.
MNT_WANTRDRW: Upgrade a mounted read-only filesystem to read-write if MNT_UPDATE is also specified.
MNT_FORCE: Force a read-write mount even if the filesystem appears to be unclean. Use of this flag can be dangerous.

The MNT_UPDATE flag indicates that the mount command is being applied to a filesystem which is already mounted. This allows the mount flags to be changed without requiring that the filesystem be unmounted and remounted. Some filesystems may not allow all flags to be changed. For example, most filesystems will not allow a change from read-write to read-only.

The type argument defines the type of the filesystem. The types of filesystems known to the system are defined in sys/mount.h . The data pointer indicates a structure that contains the type-specific arguments to mount. The types of filesystems currently supported and their type-specific data are:

Arguments for local filesystem mount calls

struct export_args {
    int     ex_flags;               /* export related flags */
    uid_t   ex_root;                /* mapping for root uid */
    struct  ucred ex_anon;          /* mapping for anonymous user */
    struct  sockaddr *ex_addr;      /* net address to which exported */
    int     ex_addrlen;             /* and the net address length */
    struct  sockaddr *ex_mask;      /* mask of valid bits in saddr */
    int     ex_masklen;             /* and the smask length */
     };


MOUNT_UFS

struct ufs_args {
    char      *fspec;               /* Block special file to mount */
    struct    export_args export;   /* network export information */
     };


MOUNT_NFS

struct nfs_args {
    struct sockaddr *addr;          /* file server address */
    int             addrlen;        /* length of address */
    int             sotype;         /* Socket type */
    int             proto;          /* and Protocol */
    u_char          *fh;            /* File handle to be mounted */
    int             fhsize;         /* Size, in bytes, of fh */
    int             flags;          /* flags */
    int             wsize;          /* write size in bytes */
    int             rsize;          /* read size in bytes */
    int             readdirsize;    /* readdir size in bytes */
    int             timeo;          /* initial timeout in .1 secs */
    int             retrans;        /* times to retry send */
    int             maxgrouplist;   /* Max. size of group list */
    int             readahead;      /* # of blocks to readahead */
    int             leaseterm;      /* Term (sec) of lease */
    int             deadthresh;     /* Retrans threshold */
    char            *hostname;      /* server's name */
     };


NFS mount option flags

     #define NFSMNT_SOFT         0x00000001  /* soft mount (hard is default) */
     #define NFSMNT_WSIZE        0x00000002  /* set write size */
     #define NFSMNT_RSIZE        0x00000004  /* set read size */
     #define NFSMNT_TIMEO        0x00000008  /* set initial timeout */
     #define NFSMNT_RETRANS      0x00000010  /* set number of request retries */
     #define NFSMNT_MAXGRPS      0x00000020  /* set maximum grouplist size */
     #define NFSMNT_INT          0x00000040  /* allow interrupts on hard mount */
     #define NFSMNT_NOCONN       0x00000080  /* Don't Connect the socket */
     #define NFSMNT_NQNFS        0x00000100  /* Use Nqnfs protocol */
     #define NFSMNT_NFSV3        0x00000200  /* Use NFS Version 3 protocol */
     #define NFSMNT_KERB         0x00000400  /* Use Kerberos authentication */
     #define NFSMNT_DUMBTIMR     0x00000800  /* Don't estimate rtt dynamically */
     #define NFSMNT_LEASETERM    0x00001000  /* set lease term (nqnfs) */
     #define NFSMNT_READAHEAD    0x00002000  /* set read ahead */
     #define NFSMNT_DEADTHRESH   0x00004000  /* set dead server retry thresh */
     #define NFSMNT_RESVPORT     0x00008000  /* Allocate a reserved port */
     #define NFSMNT_RDIRPLUS     0x00010000  /* Use Readdirplus for V3 */
     #define NFSMNT_READDIRSIZE  0x00020000  /* Set readdir size */
     #define NFSMNT_INTERNAL     0xfffc0000  /* Bits set internally */
     #define NFSMNT_HASWRITEVERF 0x00040000  /* Has write verifier for V3 */
     #define NFSMNT_GOTPATHCONF  0x00080000  /* Got the V3 pathconf info */
     #define NFSMNT_GOTFSINFO    0x00100000  /* Got the V3 fsinfo */
     #define NFSMNT_MNTD         0x00200000  /* Mnt server for mnt point */
     #define NFSMNT_DISMINPROG   0x00400000  /* Dismount in progress */
     #define NFSMNT_DISMNT       0x00800000  /* Dismounted */
     #define NFSMNT_SNDLOCK      0x01000000  /* Send socket lock */
     #define NFSMNT_WANTSND      0x02000000  /* Want above */
     #define NFSMNT_RCVLOCK      0x04000000  /* Rcv socket lock */
     #define NFSMNT_WANTRCV      0x08000000  /* Want above */
     #define NFSMNT_WAITAUTH     0x10000000  /* Wait for authentication */
     #define NFSMNT_HASAUTH      0x20000000  /* Has authenticator */
     #define NFSMNT_WANTAUTH     0x40000000  /* Wants an authenticator */
     #define NFSMNT_AUTHERR      0x80000000  /* Authentication error */


MOUNT_MSDOS

struct msdosfs_args {
     char    *fspec;       /* blocks special holding the fs to mount */
     struct  export_args export;     /* network export information */
     uid_t   uid;          /* uid that owns msdosfs files */
     gid_t   gid;          /* gid that owns msdosfs files */
     mode_t  mask;         /* mask to be applied for msdosfs perms */
     int     flags;        /* see below */
     int magic;            /* version number */
     u_int16_t u2w[128];   /* Local->Unicode table */
     u_int8_t  ul[128];    /* Local upper->lower table */
     u_int8_t  lu[128];    /* Local lower->upper table */
     u_int8_t  d2u[128];   /* DOS->local table */
     u_int8_t  u2d[128];   /* Local->DOS table */
     };

The umount function call dissociates the filesystem from the specified mount point dir .

The flags argument may specify MNT_FORCE to specify that the filesystem should be forcibly unmounted even if files are still active. Active special devices continue to work, but any further accesses to any other active files result in errors even if the filesystem is later remounted.

RETURN VALUES

If successful, mount returns a value of 0, otherwise -1 is returned and the errno variable is set to indicate the error.

If successful, umount returns a value of 0, otherwise -1 is returned and the variable errno is set to indicate the error.

ERRORS

`mount()` errors

mount() will fail when one of the following occurs:

[EPERM]: The caller is not the super-user.
[ENAMETOOLONG]: A component of a pathname exceeded 255 characters, or the entire length of a pathname exceeded 1023 characters.
[ELOOP]: Too many symbolic links were encountered in translating a pathname.
[ENOENT]: A component of dir does not exist.
[ENOTDIR]: A component of dir is not a directory, or a path prefix of fspec is not a directory.
[EBUSY]: Another process currently holds a reference to dir .
[EFAULT]: dir points outside the actor's allocated address space.

The following errors can occur for a UFS filesystem mount:

[ENODEV]: A component of ufs_args , fspec , does not exist.
[ENOTBLK]: fspec is not a block device.
[ENXIO]: The major device number of fspec is out of range (this indicates that no device driver exists for the associated hardware).
[EBUSY]: fspec is already mounted.
[EMFILE]: No space left in the mount table.
[EINVAL]: The superblock for the filesystem had a bad magic number or a block size that was out of range.
[ENOMEM]: Not enough memory was available to read the cylinder group information for the filesystem.
[EIO]: An I/O error occurred while reading the super block or cylinder group information.
[EFAULT]: fspec points outside the actor's allocated address space.

The following errors can occur for an NFS filesystem mount:

[ETIMEDOUT]: NFS timed out trying to contact the server.
[EFAULT]: Some part of the information described by nfs_args points outside the actor's allocated address space.

`umount()` errors

umount() may fail with one of the following errors:

[EPERM]: The caller is not the super-user.
[ENOTDIR]: A component of the path is not a directory.
[EINVAL]: A component of the path is not a directory.The pathname contains a character with the high-order bit set.
[ENAMETOOLONG]: A component of a pathname exceeded 255 characters, or an entire pathname exceeded 1023 characters.
[ELOOP]: Too many symbolic links were encountered in translating the pathname.
[EINVAL]: The requested directory is not in the mount table.
[EBUSY]: A process is holding a reference to a file located on the filesystem.
[EIO]: An I/O error occurred while writing cached filesystem information.

A UFS mount can also fail if the maximum number of filesystems are currently mounted.

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Interface Stability	Evolving

BUGS

Some of the error codes need translation to more obvious messages.

HISTORY

The mount and umount function calls appeared in Version 6 AT&T UNIX.

RESTRICTIONS FOR ChorusOS

Note that mfs filesystems are not supported.

ChorusOS 4.0 Last Revised December 1999