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re: bin/56631: rdump fails to back up to remote file

one problem is that the rmt protocol is kinda broken in that
there's no clear definition of what is passed to open() when
the remote processes does this.

unlike local files, dump won't pass O_CREAT to the remote
connection, so, if the file doesn't already exist it won't
be used.

from dump/dumprmt.c:

rmtopen(const char *tapedevice, int mode, int verbose)
        char buf[256];

        (void)snprintf(buf, sizeof buf, "O%s\n%d\n", tapedevice, mode);
        rmtstate = TS_OPEN;
        return (rmtcall(tapedevice, buf, verbose));

there are 3 callers:

        while (rmtopen(tape, 0, 0) < 0)
                        if (rmtopen(tape, 0, 0) >= 0) {
        while ((tapefd = (host ? rmtopen(tape, 2, 1) :

note how they pass "0" or "2" as "int mode".  what do these
0 and 2 magic numbers mean?  oh let's see in rmt(8):

from rmt/rmt.c:

                getstring(device, sizeof(device));
                getstring(mode, sizeof(mode));
                DEBUG2("rmtd: O %s %s\n", device, mode);
                tape = open(device, atoi(mode),

in other words, these values are passed to the remote host
directly as the mode argument to open().  in netbsd (and most
bsd i assume still, these days, and linux has the same in the
generic configs, but i recall there was something sysV that
changed these values):

#define O_RDONLY        0x00000000      /* open for reading only */
#define O_RDWR          0x00000002      /* open for reading and writing */

but there's no O_CREAT, so remote files are not created.


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