mount.c

linux mount的源代码

/*
 * A mount(8) for Linux 0.99.
 * mount.c,v 1.1.1.1 1993/11/18 08:40:51 jrs Exp
 *
 * Thu Jul 14 07:32:40 1994: [e-mail] added changes from Adam
 * J. Richter ([e-mail]) so that /proc/filesystems is used
 * if no -t option is given.  I modified his patches so that, if
 * /proc/filesystems is not available, the behavior of mount is the same as
 * it was previously.
 *
 * Wed Sep 14 22:43:00 1994: Mitchum DSouza
 * ([e-mail]) added support for mounting
 * the "loop" device.
 *
 * Wed Sep 14 22:55:10 1994: Sander van Malssen ([e-mail])
 * added support for remounting readonly file systems readonly.
 *
 * Wed Feb 8 09:23:18 1995: Mike Grupenhoff <[e-mail]> added
 * a probe of the superblock for the type before /proc/filesystems is
 * checked.
 *
 * Wed Feb  8 12:27:00 1995: [e-mail] fixed up error messages.
 * Sat Jun  3 20:44:38 1995: Patches from [e-mail] applied.
 * Tue Sep 26 22:38:20 1995: [e-mail], many changes
 * Fri Feb 23 13:47:00 1996: [e-mail], loop device related changes
 *
 * Fri Apr  5 01:13:33 1996: [e-mail], fixed up iso9660 autodetect
 *
 * Since then, many changes - aeb.
 *
 * Wed Oct  1 23:55:28 1997: Dick Streefland <[e-mail]>
 * Implemented the "bg", "fg" and "retry" mount options for NFS.
 *
 * Tue Aug  4 15:54:31 1998: [e-mail]:
 * Open fd 0,1,2 so that printf's do not clobber /etc/mtab or so.
 * Mangle filenames with embedded spaces. Add ufsmagic. Add locking.
 * Avoid unnecessary error messages about /proc.
 * Improve support for noncanonical names in /etc/fstab.
 */

#include <unistd.h>
#include <ctype.h>
#include <errno.h>
#include <string.h>
#include <getopt.h>
#include <stdio.h>

#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <sys/mount.h>

#include "mount_constants.h"
#include "sundries.h"
#include "mntent.h"
#include "fstab.h"
#include "lomount.h"
#include "loop.h"
#include "linux_fs.h"

#define PROC_FILESYSTEMS	"/proc/filesystems"
#define SIZE(a) (sizeof(a)/sizeof(a[0]))

#define DO_PS_FIDDLING

#ifdef DO_PS_FIDDLING
#define PROC_NAME		"mount: "
static int argc0;
static char** argv0;
static char** envp0;
extern char** environ;
#endif

/* True for fake mount (-f).  */
int fake = 0;

/* Don't write a entry in /etc/mtab (-n).  */
int nomtab = 0;

/* True for explicit readonly (-r).  */
int readonly = 0;

/* Nonzero for chatty (-v).  */
int verbose = 0;

/* Nonzero for sloppy (-s).  */
int sloppy = 0;

/* True for explicit read/write (-w).  */
int readwrite = 0;

/* True for all mount (-a).  */
int all = 0;

/* True for fork() during all mount (-F).  */
int optfork = 0;

/* True if ruid != euid.  */
int suid = 0;

/* Map from -o and fstab option strings to the flag argument to mount(2).  */
struct opt_map
{
  const char *opt;		/* option name */
  int  skip;			/* skip in mtab option string */
  int  inv;			/* true if flag value should be inverted */
  int  mask;			/* flag mask value */
};

/* Custom mount options for our own purposes.  */
/* We can use the high-order 16 bits, since the mount call
   has MS_MGC_VAL there. */
#define MS_NOAUTO	0x80000000
#define MS_USER		0x40000000
#define MS_LOOP		0x00010000

/* Options that we keep the mount system call from seeing.  */
#define MS_NOSYS	(MS_NOAUTO|MS_USER|MS_LOOP)

/* Options that we keep from appearing in the options field in the mtab.  */
#define MS_NOMTAB	(MS_REMOUNT|MS_NOAUTO|MS_USER)

/* OPTIONS that we make ordinary users have by default.  */
#define MS_SECURE	(MS_NOEXEC|MS_NOSUID|MS_NODEV)

const struct opt_map opt_map[] = {
  { "defaults",	0, 0, 0		},	/* default options */
  { "ro",	1, 0, MS_RDONLY	},	/* read-only */
  { "rw",	1, 1, MS_RDONLY	},	/* read-write */
  { "exec",	0, 1, MS_NOEXEC	},	/* permit execution of binaries */
  { "noexec",	0, 0, MS_NOEXEC	},	/* don't execute binaries */
  { "suid",	0, 1, MS_NOSUID	},	/* honor suid executables */
  { "nosuid",	0, 0, MS_NOSUID	},	/* don't honor suid executables */
  { "dev",	0, 1, MS_NODEV	},	/* interpret device files  */
  { "nodev",	0, 0, MS_NODEV	},	/* don't interpret devices */
  { "sync",	0, 0, MS_SYNCHRONOUS},	/* synchronous I/O */
  { "async",	0, 1, MS_SYNCHRONOUS},	/* asynchronous I/O */
  { "remount",  0, 0, MS_REMOUNT},      /* Alter flags of mounted FS */
  { "auto",	0, 1, MS_NOAUTO	},	/* Can be mounted using -a */
  { "noauto",	0, 0, MS_NOAUTO	},	/* Can  only be mounted explicitly */
  { "user",	0, 0, MS_USER	},	/* Allow ordinary user to mount */
  { "nouser",	0, 1, MS_USER	},	/* Forbid ordinary user to mount */
  /* add new options here */
#ifdef MS_NOSUB
  { "sub",	0, 1, MS_NOSUB	},	/* allow submounts */
  { "nosub",	0, 0, MS_NOSUB	},	/* don't allow submounts */
#endif
#ifdef MS_SILENT
  { "quiet",	0, 0, MS_SILENT    },	/* be quiet  */
  { "loud",	0, 1, MS_SILENT    },	/* print out messages. */
#endif
#ifdef MS_MANDLOCK
  { "mand",	0, 0, MS_MANDLOCK },	/* Allow mandatory locks on this FS */
  { "nomand",	0, 1, MS_MANDLOCK },	/* Forbid mandatory locks on this FS */
#endif
  { "loop",	1, 0, MS_LOOP	},	/* use a loop device */
#ifdef MS_NOATIME
  { "atime",	0, 1, MS_NOATIME },	/* Update access time */
  { "noatime",	0, 0, MS_NOATIME },	/* Do not update access time */
#endif
#ifdef MS_NODIRATIME
  { "diratime",	0, 1, MS_NODIRATIME },	/* Update dir access times */
  { "nodiratime", 0, 0, MS_NODIRATIME },/* Do not update dir access times */
#endif
  { NULL,	0, 0, 0		}
};

char *opt_loopdev, *opt_vfstype, *opt_offset, *opt_encryption;

struct string_opt_map {
  char *tag;
  int skip;
  char **valptr;
} string_opt_map[] = {
  { "loop=",	0, &opt_loopdev },
  { "vfs=",	1, &opt_vfstype },
  { "offset=",	0, &opt_offset },
  { "encryption=", 0, &opt_encryption },
  { NULL, 0, NULL }
};

static void
clear_string_opts(void) {
  struct string_opt_map *m;

  for (m = &string_opt_map[0]; m->tag; m++)
    *(m->valptr) = NULL;
}

static int
parse_string_opt(char *s) {
  struct string_opt_map *m;
  int lth;

  for (m = &string_opt_map[0]; m->tag; m++) {
    lth = strlen(m->tag);
    if (!strncmp(s, m->tag, lth)) {
      *(m->valptr) = xstrdup(s + lth);
      return 1;
    }
  }
  return 0;
}

int mount_quiet=0;

/* Report on a single mount.  */
static void
print_one (const struct mntentchn *mc) {
     if (mount_quiet)
	  return;
     printf ("%s on %s", mc->mnt_fsname, mc->mnt_dir);
     if (mc->mnt_type != NULL && *(mc->mnt_type) != '\0')
	  printf (" type %s", mc->mnt_type);
     if (mc->mnt_opts != NULL)
	  printf (" (%s)", mc->mnt_opts);
     printf ("\n");
}

/* Report on everything in mtab (of the specified types if any).  */
static int
print_all (string_list types)
{
     struct mntentchn *mc;

     for (mc = mtab_head()->nxt; mc; mc = mc->nxt) {
	  if (matching_type (mc->mnt_type, types))
	       print_one (mc);
     }
     exit (0);
}


/* Look for OPT in opt_map table and return mask value.  If OPT isn't found,
   tack it onto extra_opts (which is non-NULL).  */
static inline void
parse_opt (const char *opt, int *mask, char *extra_opts)
{
  const struct opt_map *om;

  for (om = opt_map; om->opt != NULL; om++)
    if (streq (opt, om->opt))
      {
	if (om->inv)
	  *mask &= ~om->mask;
	else
	  *mask |= om->mask;
	if (om->mask == MS_USER)
	  *mask |= MS_SECURE;
#ifdef MS_SILENT
        if (om->mask == MS_SILENT && om->inv)  {
          mount_quiet = 1;
          verbose = 0;
        }
#endif
	return;
      }
  if (*extra_opts)
    strcat(extra_opts, ",");
  strcat(extra_opts, opt);
}
  
/* Take -o options list and compute 4th and 5th args to mount(2).  flags
   gets the standard options and extra_opts anything we don't recognize.  */
static void
parse_opts (char *opts, int *flags, char **extra_opts)
{
  char *opt;

  *flags = 0;
  *extra_opts = NULL;

  clear_string_opts();

  if (opts != NULL)
    {
      *extra_opts = xmalloc (strlen (opts) + 1); 
      **extra_opts = '\0';

      for (opt = strtok (opts, ","); opt; opt = strtok (NULL, ","))
	if (!parse_string_opt (opt))
	  parse_opt (opt, flags, *extra_opts);
    }

  if (readonly)
    *flags |= MS_RDONLY;
  if (readwrite)
    *flags &= ~MS_RDONLY;
}

#if 0
/* Try to build a canonical options string.  */
static char *
fix_opts_string (int flags, char *extra_opts)
{
  const struct opt_map *om;
  const struct string_opt_map *m;
  char *new_opts;

  new_opts = (flags & MS_RDONLY) ? "ro" : "rw";
  for (om = opt_map; om->opt != NULL; om++) {
      if (om->skip)
	continue;
      if (om->inv || !om->mask || (flags & om->mask) != om->mask)
	continue;
      new_opts = xstrconcat3(new_opts, ",", om->opt);
      flags &= ~om->mask;
  }
  for (m = &string_opt_map[0]; m->tag; m++) {
      if (!m->skip && *(m->valptr))
	   new_opts = xstrconcat4(new_opts, ",", m->tag, *(m->valptr));
  }
  if (extra_opts && *extra_opts) {
      new_opts = xstrconcat3(new_opts, ",", extra_opts);
  }
  return new_opts;
}
#endif

/* Most file system types can be recognized by a `magic' number
   in the superblock.  Note that the order of the tests is
   significant: by coincidence a filesystem can have the
   magic numbers for several file system types simultaneously.
   For example, the romfs magic lives in the 1st sector;
   xiafs does not touch the 1st sector and has its magic in
   the 2nd sector; ext2 does not touch the first two sectors. */

static inline unsigned short
swapped(unsigned short a) {
     return (a>>8) | (a<<8);
}

/*
    char *fstype(const char *device);

    Probes the device and attempts to determine the type of filesystem
    contained within.

    Original routine by <[e-mail]>; made into a function
    for mount(8) by Mike Grupenhoff <[e-mail]>.
    Read the superblock only once - aeb
    Added a test for iso9660 - aeb
    Added a test for high sierra (iso9660) - [e-mail]
    Corrected the test for xiafs - aeb
    Added romfs - aeb
    Added ufs from a patch by jj. But maybe there are several types of ufs?

    Currently supports: minix, ext, ext2, xiafs, iso9660, romfs, ufs
*/
char *magic_known[] = { "minix", "ext", "ext2", "xiafs", "iso9660", "romfs",
			"ufs" };

static int
tested(const char *device) {
    char **m;

    for (m = magic_known; m - magic_known < SIZE(magic_known); m++)
        if (!strcmp(*m, device))
	    return 1;
    return 0;
}

static char *
fstype(const char *device)
{
    int fd;
    char *type = NULL;
    union {
	struct minix_super_block ms;
	struct ext_super_block es;
	struct ext2_super_block e2s;
    } sb;
    union {
	struct xiafs_super_block xiasb;
	char romfs_magic[8];
    } xsb;
    struct ufs_super_block ufssb;
    union {
	struct iso_volume_descriptor iso;
	struct hs_volume_descriptor hs;
    } isosb;
    struct stat statbuf;

    /* opening and reading an arbitrary unknown path can have
       undesired side effects - first check that `device' refers
       to a block device */
    if (stat (device, &statbuf) || !S_ISBLK(statbuf.st_mode))
      return 0;

    fd = open(device, O_RDONLY);
    if (fd < 0)
      return 0;

    if (lseek(fd, 1024, SEEK_SET) != 1024
	|| read(fd, (char *) &sb, sizeof(sb)) != sizeof(sb))
	 goto io_error;

    if (ext2magic(sb.e2s) == EXT2_SUPER_MAGIC
	|| ext2magic(sb.e2s) == EXT2_PRE_02B_MAGIC
	|| ext2magic(sb.e2s) == swapped(EXT2_SUPER_MAGIC))
	 type = "ext2";

    else if (minixmagic(sb.ms) == MINIX_SUPER_MAGIC
	     || minixmagic(sb.ms) == MINIX_SUPER_MAGIC2)
	 type = "minix";

    else if (extmagic(sb.es) == EXT_SUPER_MAGIC)
	 type = "ext";

    if (!type) {
	 if (lseek(fd, 0, SEEK_SET) != 0
	     || read(fd, (char *) &xsb, sizeof(xsb)) != sizeof(xsb))
	      goto io_error;

	 if (xiafsmagic(xsb.xiasb) == _XIAFS_SUPER_MAGIC)
	      type = "xiafs";
	 else if(!strncmp(xsb.romfs_magic, "-rom1fs-", 8))
	      type = "romfs";
    }

    if (!type) {
	 if (lseek(fd, 8192, SEEK_SET) != 8192
	     || read(fd, (char *) &ufssb, sizeof(ufssb)) != sizeof(ufssb))
	      goto io_error;

	 if (ufsmagic(ufssb) == UFS_SUPER_MAGIC) /* also test swapped version? */
	      type = "ufs";
    }

    if (!type) {
	 if (lseek(fd, 0x8000, SEEK_SET) != 0x8000
	     || read(fd, (char *) &isosb, sizeof(isosb)) != sizeof(isosb))
	      goto io_error;

	 if(strncmp(isosb.iso.id, ISO_STANDARD_ID, sizeof(isosb.iso.id)) == 0
	    || strncmp(isosb.hs.id, HS_STANDARD_ID, sizeof(isosb.hs.id)) == 0)
	      type = "iso9660";
    }

    close (fd);
    return(type);

io_error:
    perror(device);
    close(fd);
    return 0;
}

FILE *procfs;

static void
procclose(void) {
    if (procfs)
        fclose (procfs);
    procfs = 0;
}

static int
procopen(void) {
    return ((procfs = fopen(PROC_FILESYSTEMS, "r")) != NULL);
}

static char *
procnext(void) {
   char line[100];
   static char fsname[50];

   while (fgets(line, sizeof(line), procfs)) {
      if (sscanf (line, "nodev %[^\n]\n", fsname) == 1) continue;
      if (sscanf (line, " %[^ \n]\n", fsname) != 1) continue;
      return fsname;
   }
   return 0;
}

#if 0
static int
is_in_proc(char *type) {
    char *fsname;

    if (procopen()) {