[SOLVED] Linux: how to detect whether a certain partition is mounted?
lazarus / 32-Linux

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Hartmut · 2018-12-06 13:22

In a console program I want to detect, whether a certain Windows-
Partition is currently mounted, but without to change the mount-
status.

As a workaround I detect via FindFirst() whether the mounted folder is
empty or not (if it's not empty, the partition must be mounted). But
this would fail, if the mounted partition is totally empty.

How can this be done? I'm using FPC 3.0.4 on Ubuntu 18.04. Thanks in
advance.

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vincococka · 2018-12-06 13:55

One possible solution is to check /proc/mounts if it contains exact
path that you expected to be mounted.

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lucamar · 2018-12-06 14:30

Or you could use fpStatFS() and check the result for congruence.

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Hartmut · 2018-12-06 16:45

Quote from: vincococka on December 06, 2018, 02:55:28 pmOne possible
solution is to check /proc/mounts if it contains exact path that you
expected to be mounted.

I looked into file /proc/mounts and it seems to work. But I'm afraid
to "disturb" the Operating System when I open that file while reading:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
isMounted: boolean;   var f1: text;       s: ansistring;   begin 
 assign(f1,'/proc/mounts'); reset(f1);   while not eof(f1) do     
begin      readln(f1, s);         if pos(' /media/C ', s) > 0 then
begin close(f1); exit(true); end;      end;   close(f1); exit(false); 
 end;  
What do the experts say? Is this "dangerous" or not?


Quote from: lucamar on December 06, 2018, 03:30:52 pmOr you could use
fpStatFS() and check the result for congruence.

I tried function fpStatFS from Unit Unix:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
Test_fpStatFS;   var info: TStatFs;       i: longint;   begin 
 fillchar(info,sizeof(info),0);   i:=fpStatFS('/media/C/', @info);  
  writeln('i=', i);   end;  
Result 'i' was always 0.

if mounted =>
INFO={FSTYPE = 1702057286, BSIZE = 4096, BLOCKS = 1048233, BFREE =
106248, BAVAIL = 106248, FILES = 457760, FFREE = 438097, FSID = {0,
0}, NAMELEN = 255, FRSIZE = 4096, SPARE = {4142, 0, 0, 0, 0}}

if not mounted =>
INFO={FSTYPE = 61267, BSIZE = 4096, BLOCKS = 6417977, BFREE = 1245557,
BAVAIL = 913781, FILES = 1638400, FFREE = 1111304, FSID =
{-1900541924, -1966772697}, NAMELEN = 255, FRSIZE = 4096, SPARE =
{4128, 0, 0, 0, 0}}

How do you think that I can distinguish mounted state and not mounted
state?

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lucamar · 2018-12-06 19:12

Quote from: Hartmut on December 06, 2018, 05:45:43 pmIs this
"dangerous" or not?
No, it's not dangerous unless you try to lock it for too much time.
Think that it's there precisely to be able to do what you are doing.
Although you may as well "slurp" the whole file in one pass and then
search into the buffer, if just to minimize file operations.

QuoteI tried function fpStatFS from Unit Unix:
[. . .]
How do you think that I can distinguish mounted state and not mounted
state?
Well, to start with: the filesystem type is different, the number of
blocks is different, etc. I don't know off the top of ny head how to
parse FSType but a man invocation or a search in the kernel docs
should tell you that. Let me have a look, I'll be back in a jiffy...
There and back again ...

OK, here is (part of) what man statfs has to say about fstype:
Code: [Select]File system types:
              [. . .]
              EXT_SUPER_MAGIC       0x137D
              EXT2_OLD_SUPER_MAGIC  0xEF51
              EXT2_SUPER_MAGIC      0xEF53
              EXT3_SUPER_MAGIC      0xEF53
              EXT4_SUPER_MAGIC      0xEF53
              HFS_SUPER_MAGIC       0x4244
              HPFS_SUPER_MAGIC      0xF995E849
              [. . .]
              MSDOS_SUPER_MAGIC     0x4d44
              NCP_SUPER_MAGIC       0x564c
              NFS_SUPER_MAGIC       0x6969
              NTFS_SB_MAGIC         0x5346544e
              [. . .]
Just with that you can know whether the path is still in an EXTx
partition or an NTFS (or many others!) one.

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Hartmut · 2018-12-06 20:21

Thanks again for your help! No I understood: when the partition is not
mounted, I get FSTYPE = 61267 = 0xef53 which means:

EXT2_SUPER_MAGIC      0xef53
EXT3_SUPER_MAGIC      0xef53
EXT4_SUPER_MAGIC      0xef53
          
This is because folder '/media/C/' is not mounted and that folder is
part of the etx4 filesystem of Ubuntu. If folder '/media/C/' is
mounted, I get FSTYPE = 1702057286 = 0x65735546 which means:

FUSE_SUPER_MAGIC      0x65735546

Quote from: lucamar on December 06, 2018, 08:12:39 pmAlthough you may
as well "slurp" the whole file in one pass and then search into the
buffer, if just to minimize file operations.
Do you mean: read that file in binary mode into an ansistring and then
search in that ansistring with pos() like:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
readFile_string(filespec: ansistring; var s: ansistring): boolean; 
 {reads file 'filespec' into var 's'}   var f1: file;       size:
int64;   begin   assign(f1,filespec); reset(f1,1); 
 size:=filesize(f1);    try    SetLength(s,size);   except close(f1);
{if not enough memory}          SetLength(s,0);          exit(false); 
 end;    if size > 0 then blockread(f1, s[1],size); {0 => "Range check
error"}   close(f1);   exit(true);   end;

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lucamar · 2018-12-06 21:37

Quote from: Hartmut on December 06, 2018, 09:21:37 pmQuote from:
lucamar on December 06, 2018, 08:12:39 pmAlthough you may as well
"slurp" the whole file in one pass and then search into the buffer, if
just to minimize file operations.
Do you mean: read that file in binary mode into an ansistring and then
search in that ansistring with pos() like:

[... some code ...]

Well, yes, that's one way. Or use a (buffered) stream, or even a
TStringList. But you got the point: since it's usually rather small
(mine's never more than ~2 Kb, negligible) it's better to load it
whole in memory and close the file as quickly as possible.

Incidentally, I've taken the liberty of modifying your code a tiny
bit:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
readFile_string(filespec: ansistring; var s: ansistring): boolean; 
 {reads file 'filespec' into var 's'}var  f1: file;  size:
int64;begin  assign(f1,filespec);  reset(f1,1);  try   
size:=filesize(f1);    if size > 0 then begin      try       
SetLength(s, size);      except        close(f1); {if not enough
memory}        {               .^.         You should make *sure*
whether the problem is really NEM        }        s := ''       
Exit(false);      end;      blockread(f1, s[1], size); {0 => "Range
check error"}  end else    s := '';  finally      close(f1);  end; 
Result := true;end;

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Hartmut · 2018-12-07 18:51

The result of this Topic are 2 good solutions:
 - checking file /proc/mounts for the expected path to be mounted or
 - calling function fpStatFS() from unit Unix and checking the magic
codes in field INFO.FSTYPE

Thanks a lot to all who helped me.