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md: use prestaged mfs_root

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On PowerNV systems, the rootfs is passed through kexec, which loads the rootfs
into memory and set two fdt entries to describe where the file is located in
the memory;

I need to pass this memory region to the md device as a mfs_root, but, current
md driver does not support two things:

 * Just getting a pointer from an external (bootloader) memory. If I need to
workaround it, I would need to declare a static array and memcopy from this
external memory to this static variable.

 * The size of the image. The usage of mfs_root_end, which is not a pointer,
seems to be not possible for this prestaged scenario.

This patch simply adds a new way to load mfs_root from memory.

Differential Revision: https://reviews.freebsd.org/D15625
Approved by: kib, jhibbits (mentor)
This commit is contained in:
Breno Leitao 2018-06-07 13:57:34 +00:00
parent 16e05b3275
commit 7b2c7b92be
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=334784
3 changed files with 12 additions and 0 deletions
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3
sys/conf/NOTES
View File

@ -1111,6 +1111,9 @@ options MD_ROOT
# Write-protect the md root device so that it may not be mounted writeable.
options MD_ROOT_READONLY
# Allow to read MD image from external memory regions
options MD_ROOT_MEM
# Disk quotas are supported when this option is enabled.
options QUOTA #enable disk quotas

1
sys/conf/options
View File

@ -168,6 +168,7 @@ MD_ROOT opt_md.h
MD_ROOT_FSTYPE opt_md.h
MD_ROOT_READONLY opt_md.h
MD_ROOT_SIZE opt_md.h
MD_ROOT_MEM opt_md.h
MFI_DEBUG opt_mfi.h
MFI_DECODE_LOG opt_mfi.h
MPROF_BUFFERS opt_mprof.h

8
sys/dev/md/md.c
View File

@ -180,6 +180,10 @@ SYSCTL_INT(_vm, OID_AUTO, md_malloc_wait, CTLFLAG_RW, &md_malloc_wait, 0,
*/
u_char mfs_root[MD_ROOT_SIZE*1024] __attribute__ ((section ("oldmfs")));
const int mfs_root_size = sizeof(mfs_root);
#elif defined(MD_ROOT_MEM)
/* MD region already mapped in the memory */
u_char *mfs_root;
int mfs_root_size;
#else
extern volatile u_char __weak_symbol mfs_root;
extern volatile u_char __weak_symbol mfs_root_end;
@ -2074,8 +2078,12 @@ g_md_init(struct g_class *mp __unused)
#ifdef MD_ROOT
if (mfs_root_size != 0) {
sx_xlock(&md_sx);
#ifdef MD_ROOT_MEM
md_preloaded(mfs_root, mfs_root_size, NULL);
#else
md_preloaded(__DEVOLATILE(u_char *, &mfs_root), mfs_root_size,
NULL);
#endif
sx_xunlock(&md_sx);
}
#endif