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Use a platform-independent constant for PKG_MAX_SIZE.

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This constant determines the number of rights libnv will attempt to
transmit in a given control message.  In practice, the upper limit
defined by the kernel is machine-dependent and is smaller on 64-bit
kernels than on 32-bit kernels.  To ensure that a 32-bit libnv works
as expected when run on a 64-bit kernel, use a limit that will work
on both 32-bit and 64-bit kernels.

PR:		238511
Discussed with:	oshogbo
MFC after:	3 days
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D20942
This commit is contained in:
markj 2019-07-16 16:28:50 +00:00
parent a0c215448b
commit 9c639de682
1 changed files with 7 additions and 1 deletions
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8
lib/libnv/msgio.c
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@ -63,7 +63,13 @@ __FBSDID("$FreeBSD$");
/* Linux: arbitrary size, but must be lower than SCM_MAX_FD. */
#define PKG_MAX_SIZE ((64U - 1) * CMSG_SPACE(sizeof(int)))
#else
#define PKG_MAX_SIZE (MCLBYTES / CMSG_SPACE(sizeof(int)) - 1)
/*
* To work around limitations in 32-bit emulation on 64-bit kernels, use a
* machine-independent limit on the number of FDs per message. Each control
* message contains 1 FD and requires 12 bytes for the header, 4 pad bytes,
* 4 bytes for the descriptor, and another 4 pad bytes.
*/
#define PKG_MAX_SIZE (MCLBYTES / 24)
#endif
static int