For Unix Sockets , there is the struct sockaddress_un which has two members : sun_family which refers to the communication domain in which the socket is to be created and sun_path which refers to the path name
Can someone explain the meaning of the words in bold ??
Why is the rationale for naming the two members : sun_family & sun_path
What does the un in sockaddress_un mean ??
For the communication domain you might want to look at where the macro for AF_UNIX (which is mentioned in /usr/include/un.h) is set, using grep -FR AF_UNIX /usr/include/. On my system/usr/include/x86_64-linux-gnu/bits/socket.h` gives:
/* Protocol families. */
#define PF_UNSPEC 0 /* Unspecified. */
#define PF_LOCAL 1 /* Local to host (pipes and file-domain). */
#define PF_UNIX PF_LOCAL /* POSIX name for PF_LOCAL. */
#define PF_FILE PF_LOCAL /* Another non-standard name for PF_LOCAL. */
#define PF_INET 2 /* IP protocol family. */
#define PF_AX25 3 /* Amateur Radio AX.25. */
#define PF_IPX 4 /* Novell Internet Protocol. */
#define PF_APPLETALK 5 /* Appletalk DDP. */
#define PF_NETROM 6 /* Amateur radio NetROM. */
#define PF_BRIDGE 7 /* Multiprotocol bridge. */
#define PF_ATMPVC 8 /* ATM PVCs. */
#define PF_X25 9 /* Reserved for X.25 project. */
#define PF_INET6 10 /* IP version 6. */
#define PF_ROSE 11 /* Amateur Radio X.25 PLP. */
...
Which indicates that the domain is the type of communication that the socket is handling.
The un stands for unified as this combines the different additional informations (port number, path, pipe, etc) these different domains use, the specifics of which are passed in the sun_path part of the struct sockaddr_un.
Related
The MTD driver placed inside the Linux kernel source has a definition as below.
struct mtd_info_user {
__u8 type;
__u32 flags;
__u32 size; /* Total size of the MTD */
__u32 erasesize;
__u32 writesize;
__u32 oobsize; /* Amount of OOB data per block (e.g. 16) */
__u64 padding; /* Old obsolete field; do not use */
};
I'm trying to understand what the flags field stands for. My ultimate purpose is to find a way to check if the external MTD device is healthy. I thought that the flags field can represent the actual status of the device.
Inside the mtdchar_open(..) function from mtdchar.c source code, there is a comparison as below.
/* You can't open it RW if it's not a writeable device */
if ((file->f_mode & FMODE_WRITE) && !(mtd->flags & MTD_WRITEABLE)) {
ret = -EACCES;
goto out1;
}
So, I guess the flags field can be evaluated by using the macros from the mtd-abi.h header.
#define MTD_ABSENT 0
#define MTD_RAM 1
#define MTD_ROM 2
#define MTD_NORFLASH 3
#define MTD_NANDFLASH 4 /* SLC NAND */
#define MTD_DATAFLASH 6
#define MTD_UBIVOLUME 7
#define MTD_MLCNANDFLASH 8 /* MLC NAND (including TLC) */
#define MTD_WRITEABLE 0x400 /* Device is writeable */
#define MTD_BIT_WRITEABLE 0x800 /* Single bits can be flipped */
#define MTD_NO_ERASE 0x1000 /* No erase necessary */
#define MTD_POWERUP_LOCK 0x2000 /* Always locked after reset */
The problem is about why some of those definitions are declared like normal integers, e.g. MTD_ABSENT.
I have a node script I pass a large json stream into as command line arg. It's worth noting I am running Mac OSX High Sierra
The script is unable to run because of this error:
-bash: /usr/local/bin/node: Argument list too long
Upon reading, this is caused my a limit in the ARG_MAX or MAX_ARG_STRLEN
according to https://www.in-ulm.de/~mascheck/various/argmax/
I attempted to raise these limits in the config file here /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/syslimits.h
Here is a section of the file where I have raised the ARG_MAX size from (256 * 1024) and I have added the MAX_ARG_STRLEN config.
#define ARG_MAX (512 * 1024) /* max bytes for an exec function */
#define MAX_ARG_STRLEN (PAGE_SIZE * 64)
#if !defined(_POSIX_C_SOURCE) || defined(_DARWIN_C_SOURCE)
#define CHILD_MAX 266 /* max simultaneous processes */
#define GID_MAX 2147483647U /* max value for a gid_t (2^31-2) */
#endif /* (_POSIX_C_SOURCE && !_DARWIN_C_SOURCE) */
#define LINK_MAX 32767 /* max file link count */
#define MAX_CANON 1024 /* max bytes in term canon input line */
#define MAX_INPUT 1024 /* max bytes in terminal input */
#define NAME_MAX 255 /* max bytes in a file name */
#define NGROUPS_MAX 16 /* max supplemental group id's */
#if !defined(_POSIX_C_SOURCE) || defined(_DARWIN_C_SOURCE)
#define UID_MAX 2147483647U /* max value for a uid_t (2^31-2) */
#define OPEN_MAX 10240 /* max open files per process - todo, make a config option? */
#endif /* (_POSIX_C_SOURCE && !_DARWIN_C_SOURCE) */
#define PATH_MAX 1024 /* max bytes in pathname */
#define PIPE_BUF 512 /* max bytes for atomic pipe writes */
#define BC_BASE_MAX 99 /* max ibase/obase values in bc(1) */
#define BC_DIM_MAX 2048 /* max array elements in bc(1) */
#define BC_SCALE_MAX 99 /* max scale value in bc(1) */
#define BC_STRING_MAX 1000 /* max const string length in bc(1) */
#define CHARCLASS_NAME_MAX 14 /* max character class name size */
#define COLL_WEIGHTS_MAX 2 /* max weights for order keyword */
#define EQUIV_CLASS_MAX 2
#define EXPR_NEST_MAX 32 /* max expressions nested in expr(1) */
#define LINE_MAX 2048 /* max bytes in an input line */
#define RE_DUP_MAX 255 /* max RE's in interval notation */
#if __DARWIN_UNIX03
#define NZERO 20 /* default priority [XSI] */
/* = ((PRIO_MAX - PRIO_MIN) / 2) + 1 */
/* range: 0 - 39 [(2 * NZERO) - 1] */
/* 0 is not actually used */
#else /* !__DARWIN_UNIX03 */
#define NZERO 0 /* default priority */
/* range: -20 - 20 */
/* (PRIO_MIN - PRIO_MAX) */
#endif /* __DARWIN_UNIX03 */
#endif /* !_ANSI_SOURCE */
#endif /* !_SYS_SYSLIMITS_H_ */
After these changes, my file which contains 330,000 characters is still failing. The file is 300kb upon running the node script.
Your expertise is appreciated! I am unsure if this is caused by an overflow in the string size or the arg size (what is the difference?) Either way I have not found a way to make it work
These values cannot be changed in Mac OS X kernel.
It was strange to me when I saw this:
#define HI3518_IOCH1_PHYS 0x10000000 /* 0x1000_0000 ~ 0x1020_0000 */
#define HI3518_IOCH2_PHYS 0x20000000 /* 0x2000_0000 ~ 0x2020_0000 */
#define HI3518_IOCH1_SIZE 0x200000
#define HI3518_IOCH2_SIZE 0x700000
#define HI3518_IOCH1_VIRT 0xFE000000
#define HI3518_IOCH2_VIRT (HI3518_IOCH1_VIRT + HI3518_IOCH1_SIZE)
This is located at arch/arm/mach-hi3518/include/mach/io.h
The last 2 line puzzle me, is that mean user can determine the virtual address themselves, don't need to use APIs?
Thanks in advance!
I have following code to get width and height of screen in Linux.
#ifdef TIOCGSIZE
struct ttysize ts;
ioctl(STDIN_FILENO, TIOCGSIZE, &ts);
cols = ts.ts_cols;
lines = ts.ts_lines;
#elif defined(TIOCGWINSZ)
struct winsize ts;
ioctl(STDIN_FILENO, TIOCGWINSZ, &ts);
cols = ts.ws_col;
lines = ts.ws_row;
#endif /* TIOCGSIZE */
What is difference between ttysize and winsize?
The ttysize was the original implementation for SunOS 3.0 (February 1986), and soon after made obsolete by winsize, which adds the size of the window in pixels. Here's
what the definitions look like in <sys/ttycom.h> from SunOS 4:
/*
* Window/terminal size structure.
* This information is stored by the kernel
* in order to provide a consistent interface,
* but is not used by the kernel.
*
* Type must be "unsigned short" so that types.h not required.
*/
struct winsize {
unsigned short ws_row; /* rows, in characters */
unsigned short ws_col; /* columns, in characters */
unsigned short ws_xpixel; /* horizontal size, pixels - not used */
unsigned short ws_ypixel; /* vertical size, pixels - not used */
};
#define TIOCGWINSZ _IOR(t, 104, struct winsize) /* get window size */
#define TIOCSWINSZ _IOW(t, 103, struct winsize) /* set window size */
/*
* Sun version of same.
*/
struct ttysize {
int ts_lines; /* number of lines on terminal */
int ts_cols; /* number of columns on terminal */
};
#define TIOCSSIZE _IOW(t,37,struct ttysize)/* set tty size */
#define TIOCGSIZE _IOR(t,38,struct ttysize)/* get tty size */
The data types are different (an integer would waste memory), and the fields have different names.
The ttysize structure has long been obsolete: if either is provided by the system, winsize is supported. That wasn't true when porting ncurses to SCO OpenServer in 1997, as noted in this chunk from lib_setup.c:
/*
* SCO defines TIOCGSIZE and the corresponding struct. Other systems (SunOS,
* Solaris, IRIX) define TIOCGWINSZ and struct winsize.
*/
#ifdef TIOCGSIZE
# define IOCTL_WINSIZE TIOCGSIZE
# define STRUCT_WINSIZE struct ttysize
# define WINSIZE_ROWS(n) (int)n.ts_lines
# define WINSIZE_COLS(n) (int)n.ts_cols
#else
# ifdef TIOCGWINSZ
# define IOCTL_WINSIZE TIOCGWINSZ
# define STRUCT_WINSIZE struct winsize
# define WINSIZE_ROWS(n) (int)n.ws_row
# define WINSIZE_COLS(n) (int)n.ws_col
# endif
#endif
You might notice that Linux is not mentioned in the comment. According to comments in asm-sparc64/ioctls.h, the ioctl for ttysize was unsupported as of 2.6.16:
/* Note that all the ioctls that are not available in Linux have a
* double underscore on the front to: a) avoid some programs to
* think we support some ioctls under Linux (autoconfiguration stuff)
*/
...
#define TIOCCONS _IO('t', 36)
#define __TIOCSSIZE _IOW('t', 37, struct sunos_ttysize) /* SunOS Specific */
#define __TIOCGSIZE _IOR('t', 38, struct sunos_ttysize) /* SunOS Specific */
#define TIOCGSOFTCAR _IOR('t', 100, int)
#define TIOCSSOFTCAR _IOW('t', 101, int)
#define __TIOCUCNTL _IOW('t', 102, int) /* SunOS Specific */
#define TIOCSWINSZ _IOW('t', 103, struct winsize)
#define TIOCGWINSZ _IOR('t', 104, struct winsize)
A much earlier comment in 1995 added the definitions (without the double-underscore). Possibly a few programs used that with Linux, although winsize was well established on most platforms before Linux was begun. A little more digging finds that the double-underscore was introduced in 1996 (patch-2.1.9 linux/include/asm-sparc/ioctls.h). Given that, very few programs would have used it with Linux.
Further reading:
Garbage-collect struct ttysize (OpenBSD mailing list)
/dev/console MKS manual page
They have the same function (at least in this case - maybe one structure has an additional field not used here).
Historically some (mainly older) Linux versions have different definitions of the IOCTL codes. Therefore some Linux versions have only TIOCGSIZE defined (using a ttysize structure) and some Linux versions have only TIOCGWINSZ defined.
Using the "#ifdef" construction the program can be compiled for both Linux versions.
Newer Linux versions should have both IOCTLs defined.
I am reading source code of xl2tpd, and face lots of problems when reading this code. For example I cannot find where the structure lac is defined. How do I find the definition of this structure?
I have used ctags and vim to read this code, but failed to find the structure. I googled and could not find the structure. Is there any method that can make the code reading process more comfortable? That is, I can jump to definition of most variables, functions and structures?
try cscope with vim. follow steps below -
1) run cscope -R in xl2tpd directory . it will create file cscope.out
2) open file with vim where structure lac is used
3) use :cs f g <lac> . now it will show the files where lac is defined .
4) choose file.h. it contain the definition .
if you are perticulerly interested in definition of struct lac it is below -
struct lac
{
struct lac *next;
struct host *lns; /* LNS's we can connect to */
struct schedule_entry *rsched;
int tun_rws; /* Receive window size (tunnel) */
int call_rws; /* Call rws */
int rxspeed; /* Tunnel rx speed */
int txspeed; /* Tunnel tx speed */
int active; /* Is this connection in active use? */
int hbit; /* Permit hidden AVP's? */
int lbit; /* Use the length field? */
int challenge; /* Challenge authenticate the peer? */
unsigned int localaddr; /* Local IP address */
unsigned int remoteaddr; /* Force remote address to this */
char authname[STRLEN]; /* Who we authenticate as */
char password[STRLEN]; /* Password to authenticate with */
char peername[STRLEN]; /* Force peer name to this */
char hostname[STRLEN]; /* Hostname to report */
char entname[STRLEN]; /* Name of this entry */
int authpeer; /* Authenticate our peer? */
int authself; /* Authenticate ourselves? */
int pap_require; /* Require PAP auth for PPP */
int chap_require; /* Require CHAP auth for PPP */
int pap_refuse; /* Refuse PAP authentication for us */
int chap_refuse; /* Refuse CHAP authentication for us */
int idle; /* Idle timeout in seconds */
int autodial; /* Try to dial immediately? */
int defaultroute; /* Use as default route? */
int redial; /* Redial if disconnected */
int rmax; /* Maximum # of consecutive redials */
int rtries; /* # of tries so far */
int rtimeout; /* Redial every this many # of seconds */
char pppoptfile[STRLEN]; /* File containing PPP options */
int debug;
struct tunnel *t; /* Our tunnel */
struct call *c; /* Our call */
};
When going through third-party code, there are a few tools that I have found invaluable:
Source Navigator
lxr
ctags
and, of course, the oldest and greatest of all: grep
I believe that the Eclipse CDT also allows you to quickly find the definition of any variable you are looking at, but I have not actually used it - I prefer using console programs for my actual C coding.
None of those are vim-based, although at least ctags can be used via vim or emacs. Nevertheless, they can be very useful when exploring a new codebase that you know nothing about...
Are you talking about this?
The source code already comes with a tags file.
Loading any file (common.h in my case) in Vim you can use :tag lac to jump to the first definition of lac or :tselect lac to choose between the 3 occurrences in this project and :tag gconfig to jump to the unique definition of gconfig.
See :help tags.
I'm using vim + cscope and have the same issue with you. I find a way to workaround this issue.
in vim, search the text instead of the definition. for example, in the linux kernel source code, if you're trying to find "struct file",
commands this:
cs find t struct file {
you will have a accurate definition timely in most cases, take care, no quotation mark for the text "struct file {".
hope it will help you.