man3/getmntent.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .\" References consulted:
   6 .\"     Linux libc source code
   7 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
   8 .\"     386BSD man pages
   9 .\" Modified Sat Jul 24 21:46:57 1993 by Rik Faith (faith@cs.unc.edu)
  10 .\" Modified 961109, 031115, aeb
  11 .\"
  12 .TH getmntent 3 (date) "Linux man-pages (unreleased)"
  13 .SH NAME
  14 getmntent, setmntent, addmntent, endmntent, hasmntopt,
  15 getmntent_r \- get filesystem descriptor file entry
  16 .SH LIBRARY
  17 Standard C library
  18 .RI ( libc ", " \-lc )
  19 .SH SYNOPSIS
  20 .nf
  21 .B #include <stdio.h>
  22 .B #include <mntent.h>
  23 .PP
  24 .BI "FILE *setmntent(const char *" filename ", const char *" type );
  25 .PP
  26 .BI "struct mntent *getmntent(FILE *" stream );
  27 .PP
  28 .BI "int addmntent(FILE *restrict " stream ,
  29 .BI "              const struct mntent *restrict " mnt );
  30 .PP
  31 .BI "int endmntent(FILE *" streamp );
  32 .PP
  33 .BI "char *hasmntopt(const struct mntent *" mnt ", const char *" opt );
  34 .PP
  35 /* GNU extension */
  36 .B #include <mntent.h>
  37 .PP
  38 .BI "struct mntent *getmntent_r(FILE *restrict " streamp ,
  39 .BI "              struct mntent *restrict " mntbuf ,
  40 .BI "              char *restrict " buf ", int " buflen );
  41 .fi
  42 .PP
  43 .RS -4
  44 Feature Test Macro Requirements for glibc (see
  45 .BR feature_test_macros (7)):
  46 .RE
  47 .PP
  48 .BR getmntent_r ():
  49 .nf
  50     Since glibc 2.19:
  51         _DEFAULT_SOURCE
  52     Glibc 2.19 and earlier:
  53         _BSD_SOURCE || _SVID_SOURCE
  54 .fi
  55 .SH DESCRIPTION
  56 These routines are used to access the filesystem description file
  57 .I /etc/fstab
  58 and the mounted filesystem description file
  59 .IR /etc/mtab .
  60 .PP
  61 The
  62 .BR setmntent ()
  63 function opens the filesystem description file
  64 .I filename
  65 and returns a file pointer which can be used by
  66 .BR getmntent ().
  67 The argument
  68 .I type
  69 is the type of access
  70 required and can take the same values as the
  71 .I mode
  72 argument of
  73 .BR fopen (3).
  74 The returned stream should be closed using
  75 .BR endmntent ()
  76 rather than
  77 .BR fclose (3).
  78 .PP
  79 The
  80 .BR getmntent ()
  81 function reads the next line of the filesystem
  82 description file from
  83 .I stream
  84 and returns a pointer to a structure
  85 containing the broken out fields from a line in the file.
  86 The pointer
  87 points to a static area of memory which is overwritten by subsequent
  88 calls to
  89 .BR getmntent ().
  90 .PP
  91 The
  92 .BR addmntent ()
  93 function adds the
  94 .I mntent
  95 structure
  96 .I mnt
  97 to
  98 the end of the open
  99 .IR stream .
 100 .PP
 101 The
 102 .BR endmntent ()
 103 function closes the
 104 .I stream
 105 associated with the filesystem description file.
 106 .PP
 107 The
 108 .BR hasmntopt ()
 109 function scans the
 110 .I mnt_opts
 111 field (see below)
 112 of the
 113 .I mntent
 114 structure
 115 .I mnt
 116 for a substring that matches
 117 .IR opt .
 118 See
 119 .I <mntent.h>
 120 and
 121 .BR mount (8)
 122 for valid mount options.
 123 .PP
 124 The reentrant
 125 .BR getmntent_r ()
 126 function is similar to
 127 .BR getmntent (),
 128 but stores the
 129 .I mntent
 130 structure
 131 in the provided
 132 .IR *mntbuf ,
 133 and stores the strings pointed to by the entries in that structure
 134 in the provided array
 135 .I buf
 136 of size
 137 .IR buflen .
 138 .PP
 139 The
 140 .I mntent
 141 structure is defined in
 142 .I <mntent.h>
 143 as follows:
 144 .PP
 145 .in +4n
 146 .EX
 147 struct mntent {
 148     char *mnt_fsname;   /* name of mounted filesystem */
 149     char *mnt_dir;      /* filesystem path prefix */
 150     char *mnt_type;     /* mount type (see mntent.h) */
 151     char *mnt_opts;     /* mount options (see mntent.h) */
 152     int   mnt_freq;     /* dump frequency in days */
 153     int   mnt_passno;   /* pass number on parallel fsck */
 154 };
 155 .EE
 156 .in
 157 .PP
 158 Since fields in the mtab and fstab files are separated by whitespace,
 159 octal escapes are used to represent the characters space (\e040),
 160 tab (\e011), newline (\e012), and backslash (\e\e) in those files
 161 when they occur in one of the four strings in a
 162 .I mntent
 163 structure.
 164 The routines
 165 .BR addmntent ()
 166 and
 167 .BR getmntent ()
 168 will convert
 169 from string representation to escaped representation and back.
 170 When converting from escaped representation, the sequence \e134 is
 171 also converted to a backslash.
 172 .SH RETURN VALUE
 173 The
 174 .BR getmntent ()
 175 and
 176 .BR getmntent_r ()
 177 functions return
 178 a pointer to the
 179 .I mntent
 180 structure or NULL on failure.
 181 .PP
 182 The
 183 .BR addmntent ()
 184 function returns 0 on success and 1 on failure.
 185 .PP
 186 The
 187 .BR endmntent ()
 188 function always returns 1.
 189 .PP
 190 The
 191 .BR hasmntopt ()
 192 function returns the address of the substring if
 193 a match is found and NULL otherwise.
 194 .SH FILES
 195 .TP
 196 .I /etc/fstab
 197 filesystem description file
 198 .TP
 199 .I /etc/mtab
 200 mounted filesystem description file
 201 .SH ATTRIBUTES
 202 For an explanation of the terms used in this section, see
 203 .BR attributes (7).
 204 .ad l
 205 .nh
 206 .TS
 207 allbox;
 208 lb lb lbx
 209 l l l.
 210 Interface       Attribute       Value
 211 T{
 212 .BR setmntent (),
 213 .BR endmntent (),
 214 .BR hasmntopt ()
 215 T}      Thread safety   MT-Safe
 216 T{
 217 .BR getmntent ()
 218 T}      Thread safety   T{
 219 MT-Unsafe race:mntentbuf locale
 220 T}
 221 T{
 222 .BR addmntent ()
 223 T}      Thread safety   T{
 224 MT-Safe race:stream locale
 225 T}
 226 T{
 227 .BR getmntent_r ()
 228 T}      Thread safety   MT-Safe locale
 229 .TE
 230 .hy
 231 .ad
 232 .sp 1
 233 .SH STANDARDS
 234 The nonreentrant functions are from SunOS 4.1.3.
 235 A routine
 236 .BR getmntent_r ()
 237 was introduced in HP-UX 10, but it returns an
 238 .IR int .
 239 The prototype shown above is glibc-only.
 240 .SH NOTES
 241 System V also has a
 242 .BR getmntent ()
 243 function but the calling sequence
 244 differs, and the returned structure is different.
 245 Under System V
 246 .I /etc/mnttab
 247 is used.
 248 4.4BSD and Digital UNIX have a routine
 249 .BR getmntinfo (),
 250 a wrapper around the system call
 251 .BR getfsstat ().
 252 .SH SEE ALSO
 253 .BR fopen (3),
 254 .BR fstab (5),
 255 .BR mount (8)