[v3] Allow using special files with File I/O functions

  - Remove the restriction to regular files only and add support for special file
types in the File IO stat structure.
- Define a few more macro definitions of file types such as FIFOs, etc.

The major goal is being able to write advanced embedded testing functions, like:
- using a FIFO between the embedded program and the host, instead of being
  restricted only to the GDB console.
- mocking features based on host's by opening some /dev special files.

2018-06-28  Julio Guerra  <julio@farjump.io>

        * remote-fileio.c (remote_fileio_func_open, remote_fileio_func_stat):
        Allow using File I/O functions open(), stat() and fstat() on special
        files.
        * ../include/gdb/fileio.h: Add macro definitions for special files,
        both for fst_dev and fst_mode fields of struct fst_stat.
        * common/fileio.c (fileio_to_host_mode, fileio_mode_pack): Add new
        special file types in fst_mode's definition.
        (host_to_fileio_stat): Define fst_dev using the new macro definitions
        and according to the file's type.

Signed-off-by: Julio Guerra <julio@farjump.io>
---
 gdb/ChangeLog        | 12 ++++++++
 gdb/common/fileio.c  | 66 +++++++++++++++++++++++++++++++++++---------
 gdb/remote-fileio.c  | 28 ++-----------------
 include/gdb/fileio.h | 19 +++++++++++--
 4 files changed, 83 insertions(+), 42 deletions(-)

-- 
2.18.0
  

You can find below the logs of the test I performed using our GDB server with a program embedded in a Raspberry Pi:

 

(gdb) set $st = (struct stat*) malloc(sizeof (struct stat))

(gdb) call stat("/dev/stdout", $st)
$1 = 0x0
(gdb) p *$st
$2 = {
  st_dev = 0x2, 
  st_ino = 0x4, 
  st_mode = 0x2190, 
  st_nlink = 0x1, 
  st_uid = 0x3e8, 
  st_gid = 0x5, 
  st_rdev = 0x8801, 
  st_size = 0x0, 
  st_atime = 0x5b3507e0, 
  st_spare1 = 0x0, 
  st_mtime = 0x5b34fb47, 
  st_spare2 = 0x0, 
  st_ctime = 0x0, 
  st_spare3 = 0x0, 
  st_blksize = 0x0, 
  st_blocks = 0x5b3507e0, 
  st_spare4 = {0x0, 0x0}
}
(gdb) p /o $st->st_mode            
$8 = 020620

(gdb) call stat("myfifo", $st)     
$3 = 0x0
(gdb) p *$st
$4 = {
  st_dev = 0x2, 
  st_ino = 0x4f7c, 
  st_mode = 0x11a4, 
  st_nlink = 0x1, 
  st_uid = 0x3e8, 
  st_gid = 0x3e8, 
  st_rdev = 0x0, 
  st_size = 0x0, 
  st_atime = 0x5b3504ed, 
  st_spare1 = 0x0, 
  st_mtime = 0x5b3504ed, 
  st_spare2 = 0x0, 
  st_ctime = 0x0, 
  st_spare3 = 0x0, 
  st_blksize = 0x0, 
  st_blocks = 0x5b3504ed, 
  st_spare4 = {0x0, 0x0}
}
(gdb) p /o $st->st_mode       
$6 = 010644

(gdb) call stat("/run/dbus/system_bus_socket", $st)  
$9 = 0x0
(gdb) p *$st                                       
$10 = {
  st_dev = 0x2, 
  st_ino = 0x36c7, 
  st_mode = 0xc1b6, 
  st_nlink = 0x1, 
  st_uid = 0x0, 
  st_gid = 0x0, 
  st_rdev = 0x0, 
  st_size = 0x0, 
  st_atime = 0x5b33e995, 
  st_spare1 = 0x0, 
  st_mtime = 0x5b33e995, 
  st_spare2 = 0x0, 
  st_ctime = 0x0, 
  st_spare3 = 0x0, 
  st_blksize = 0x0, 
  st_blocks = 0x5b33e995, 
  st_spare4 = {0x0, 0x0}
}
(gdb) p /o $st->st_mode                            
$11 = 0140666

(gdb) call stat("/tmp", $st)                       
$12 = 0x0
(gdb) p *$st                
$13 = {
  st_dev = 0x2, 
  st_ino = 0x7a5, 
  st_mode = 0x41ff, 
  st_nlink = 0x1, 
  st_uid = 0x0, 
  st_gid = 0x0, 
  st_rdev = 0x0, 
  st_size = 0x0, 
  st_atime = 0x5b350829, 
  st_spare1 = 0x0, 
  st_mtime = 0x5b350829, 
  st_spare2 = 0x0, 
  st_ctime = 0x0, 
  st_spare3 = 0x0, 
  st_blksize = 0x0, 
  st_blocks = 0x5a5a9802, 
  st_spare4 = {0x0, 0x0}
}
(gdb) p /o $st->st_mode     
$14 = 040777

(gdb) call stat("Makefile", $st)
$15 = 0x0
(gdb) p *$st                    
$16 = {
  st_dev = 0x0, 
  st_ino = 0xc6b9, 
  st_mode = 0x81a4, 
  st_nlink = 0x1, 
  st_uid = 0x3e8, 
  st_gid = 0x3e8, 
  st_rdev = 0x0, 
  st_size = 0x0, 
  st_atime = 0x5ae35b23, 
  st_spare1 = 0x0, 
  st_mtime = 0x5b311f46, 
  st_spare2 = 0x0, 
  st_ctime = 0x0, 
  st_spare3 = 0x0, 
  st_blksize = 0x0, 
  st_blocks = 0x5b3500d5, 
  st_spare4 = {0x0, 0x0}
}
(gdb) p /o $st->st_mode         
$17 = 0100644

(gdb) call stat("i dont exist", $st)
$18 = 0xffffffff

(gdb) call fstat(0, $st)
$1 = 0x0
(gdb) p *$st
$3 = {
  st_dev = 0x1, 
  st_ino = 0x0, 
  st_mode = 0x2100, 
  st_nlink = 0x1, 
  st_uid = 0x3e8, 
  st_gid = 0x3e8, 
  st_rdev = 0x0, 
  st_size = 0x0, 
  st_atime = 0x5b35144e, 
  st_spare1 = 0x0, 
  st_mtime = 0x5b35144e, 
  st_spare2 = 0x0, 
  st_ctime = 0x0, 
  st_spare3 = 0x0, 
  st_blksize = 0x0, 
  st_blocks = 0x5b35144e, 
  st_spare4 = {0x0, 0x0}
}

(gdb) call fstat(1, $st)
$4 = 0x0
(gdb) p *$st                                               
$5 = {
  st_dev = 0x1, 
  st_ino = 0x0, 
  st_mode = 0x2080, 
  st_nlink = 0x1, 
  st_uid = 0x3e8, 
  st_gid = 0x3e8, 
  st_rdev = 0x0, 
  st_size = 0x0, 
  st_atime = 0x5b351460, 
  st_spare1 = 0x0, 
  st_mtime = 0x5b351460, 
  st_spare2 = 0x0, 
  st_ctime = 0x0, 
  st_spare3 = 0x0, 
  st_blksize = 0x0, 
  st_blocks = 0x5b351460, 
  st_spare4 = {0x0, 0x0}
}

(gdb) call fstat(2, $st)
$6 = 0x0
(gdb) p *$st            
$7 = {
  st_dev = 0x1, 
  st_ino = 0x0, 
  st_mode = 0x2080, 
  st_nlink = 0x1, 
  st_uid = 0x3e8, 
  st_gid = 0x3e8, 
  st_rdev = 0x0, 
  st_size = 0x0, 
  st_atime = 0x5b35146b, 
  st_spare1 = 0x0, 
  st_mtime = 0x5b35146b, 
  st_spare2 = 0x0, 
  st_ctime = 0x0, 
  st_spare3 = 0x0, 
  st_blksize = 0x0, 
  st_blocks = 0x5b35146b, 
  st_spare4 = {0x0, 0x0}
}

(gdb) call fstat(3, $st)
$8 = 0xffffffff

(gdb) set $fd = open("myfifo", 0)
(gdb) call fstat($fd, $st)       
$10 = 0x0
(gdb) p *$st
$12 = {
  st_dev = 0x2, 
  st_ino = 0x4f7c, 
  st_mode = 0x11a4, 
  st_nlink = 0x1, 
  st_uid = 0x3e8, 
  st_gid = 0x3e8, 
  st_rdev = 0x0, 
  st_size = 0x0, 
  st_atime = 0x5b351511, 
  st_spare1 = 0x0, 
  st_mtime = 0x5b351511, 
  st_spare2 = 0x0, 
  st_ctime = 0x0, 
  st_spare3 = 0x0, 
  st_blksize = 0x0, 
  st_blocks = 0x5b3504ed, 
  st_spare4 = {0x0, 0x0}
}
(gdb) p /o $st->st_mode
$13 = 010644
  

On 06/28/2018 08:27 PM, Julio Guerra wrote:
> - Remove the restriction to regular files only and add support for special file
> types in the File IO stat structure.
> - Define a few more macro definitions of file types such as FIFOs, etc.
> 
> The major goal is being able to write advanced embedded testing functions, like:
> - using a FIFO between the embedded program and the host, instead of being
>   restricted only to the GDB console.
> - mocking features based on host's by opening some /dev special files.
> 

This needs a GDB manual change, and a NEWS entry.

> 2018-06-28  Julio Guerra  <julio@farjump.io>
> 
>         * remote-fileio.c (remote_fileio_func_open, remote_fileio_func_stat):
>         Allow using File I/O functions open(), stat() and fstat() on special
>         files.
>         * ../include/gdb/fileio.h: Add macro definitions for special files,
>         both for fst_dev and fst_mode fields of struct fst_stat.
>         * common/fileio.c (fileio_to_host_mode, fileio_mode_pack): Add new
>         special file types in fst_mode's definition.
>         (host_to_fileio_stat): Define fst_dev using the new macro definitions
>         and according to the file's type.

Note that include/ has its own ChangeLog file.

>  2018-06-27  Simon Marchi  <simon.marchi@ericsson.com>
>  
>  	* gdb-gdb.py.in (StructMainTypePrettyPrinter) <to_string>: Don't
> diff --git a/gdb/common/fileio.c b/gdb/common/fileio.c
> index 912a7ede3c..9ee78e227c 100644
> --- a/gdb/common/fileio.c
> +++ b/gdb/common/fileio.c
> @@ -119,12 +119,31 @@ fileio_to_host_mode (int fileio_mode, mode_t *mode_p)
>    if (fileio_mode & ~FILEIO_S_SUPPORTED)
>      return -1;
>  
> -  if (fileio_mode & FILEIO_S_IFREG)
> -    mode |= S_IFREG;
> -  if (fileio_mode & FILEIO_S_IFDIR)
> -    mode |= S_IFDIR;
> -  if (fileio_mode & FILEIO_S_IFCHR)
> -    mode |= S_IFCHR;
> +  switch (fileio_mode & FILEIO_S_IFMT)
> +    {
> +    case FILEIO_S_IFSOCK:
> +      *mode_p |= S_IFSOCK;
> +      break;
> +    case FILEIO_S_IFLNK:
> +      mode |= S_IFLNK;
> +      break;
> +    case FILEIO_S_IFREG:
> +      mode |= S_IFREG;
> +      break;
> +    case FILEIO_S_IFBLK:
> +      mode |= S_IFBLK;
> +      break;
> +    case FILEIO_S_IFDIR:
> +      mode |= S_IFDIR;
> +      break;
> +    case FILEIO_S_IFCHR:
> +      mode |= S_IFCHR;
> +      break;
> +    case FILEIO_S_IFIFO:
> +      mode |= S_IFIFO;
> +      break;
> +    }
> +
>    if (fileio_mode & FILEIO_S_IRUSR)
>      mode |= S_IRUSR;
>    if (fileio_mode & FILEIO_S_IWUSR)
> @@ -165,12 +184,31 @@ fileio_mode_pack (mode_t mode)
>  {
>    mode_t tmode = 0;
>  
> -  if (S_ISREG (mode))
> -    tmode |= FILEIO_S_IFREG;
> -  if (S_ISDIR (mode))
> -    tmode |= FILEIO_S_IFDIR;
> -  if (S_ISCHR (mode))
> -    tmode |= FILEIO_S_IFCHR;
> +  switch (mode & S_IFMT)
> +    {
> +    case S_IFSOCK:
> +      tmode |= FILEIO_S_IFSOCK;
> +      break;
> +    case S_IFLNK:
> +      tmode |= FILEIO_S_IFLNK;
> +      break;
> +    case S_IFREG:
> +      tmode |= FILEIO_S_IFREG;
> +      break;
> +    case S_IFBLK:
> +      tmode |= FILEIO_S_IFBLK;
> +      break;
> +    case S_IFDIR:
> +      tmode |= FILEIO_S_IFDIR;
> +      break;
> +    case S_IFCHR:
> +      tmode |= FILEIO_S_IFCHR;
> +      break;
> +    case S_IFIFO:
> +      tmode |= FILEIO_S_IFIFO;
> +      break;
> +    }

I'm not sure whether all these S_FOO macros exist
on all hosts.

Looking at:
 https://www.gnu.org/software/gnulib/manual/html_node/sys_002fstat_002eh.html

gnulib's sys/stat.h (gdb/gnulib/import/sys_stat.in.h) adds some
replacements, but then I'm not sure whether checking S_IFxxx
etc. directly instead of using the S_ISxxx function-style macros
is the right thing to do portability-wise.  It may be S_ISxxx was being
used for a reason?

> +
>    if (mode & S_IRUSR)
>      tmode |= FILEIO_S_IRUSR;
>    if (mode & S_IWUSR)
> @@ -224,8 +262,10 @@ void
>  host_to_fileio_stat (struct stat *st, struct fio_stat *fst)
>  {
>    LONGEST blksize;
> +  long    fst_dev;

We don't align variable names like that.

>  
> -  host_to_fileio_uint ((long) st->st_dev, fst->fst_dev);
> +  fst_dev = S_ISREG(st->st_mode) ? FILEIO_STDEV_FILE : FILEIO_STDEV_SPECIAL;

Missing space in "S_ISREG (".

> +  host_to_fileio_uint (fst_dev, fst->fst_dev);
>    host_to_fileio_uint ((long) st->st_ino, fst->fst_ino);
>    host_to_fileio_mode (st->st_mode, fst->fst_mode);
>    host_to_fileio_uint ((long) st->st_nlink, fst->fst_nlink);
> diff --git a/gdb/remote-fileio.c b/gdb/remote-fileio.c
> index 313da642ea..837081269a 100644
> --- a/gdb/remote-fileio.c
> +++ b/gdb/remote-fileio.c
> @@ -407,24 +407,6 @@ remote_fileio_func_open (remote_target *remote, char *buf)
>        return;
>      }
>  
> -  /* Check if pathname exists and is not a regular file or directory.  If so,
> -     return an appropriate error code.  Same for trying to open directories
> -     for writing.  */

Did you intend to remove the "Same for trying to open directories
for writing." part?

Thanks,
Pedro Alves