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man pages section 9: DDI and DKI Kernel Functions

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Updated: July 2017



copymsg - copy a message


#include <sys/stream.h>

mblk_t *copymsg(mblk_t *mp);

Interface Level

Architecture independent level 1 (DDI/DKI).



Pointer to the message to be copied.


The copymsg() function forms a new message by allocating new message blocks, and copying the contents of the message referred to by mp (using the copyb(9F) function). It returns a pointer to the new message.

Return Values

If the copy is successful, copymsg() returns a pointer to the new message. Otherwise, it returns a NULL pointer.


The copymsg() function can be called from user, interrupt, or kernel context.


Example 1 : Using copymsg

The routine lctouc() converts all the lowercase ASCII characters in the message to uppercase. If the reference count is greater than one (line 8), then the message is shared, and must be copied before changing the contents of the data buffer. If the call to the copymsg() function fails (line 9), return NULL (line 10), otherwise, free the original message (line 11). If the reference count was equal to 1, the message can be modified. For each character (line 16) in each message block (line 15), if it is a lowercase letter, convert it to an uppercase letter (line 18). A pointer to the converted message is returned (line 21).

 1 mblk_t *lctouc(mp)
 2    mblk_t *mp;
 3 {
 4    mblk_t *cmp;
 5    mblk_t *tmp;
 6    unsigned char *cp;
 8    if (mp->b_datap->db_ref > 1) {
 9            if ((cmp = copymsg(mp)) == NULL)
10                     return (NULL);
11            freemsg(mp);
12    } else {
13            cmp = mp;
14    }
15    for (tmp = cmp; tmp; tmp = tmp->b_cont) {
16            for (cp = tmp->b_rptr; cp < tmp->b_wptr; cp++) {
17                    if ((*cp <= 'z') && (*cp >= 'a'))
18                             *cp -= 0x20;
19            }
20    }
21    return(cmp);
22 }

See Also

allocb(9F), copyb(9F), msgb(9S)

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