This patch contains the code that enables us to access the previous kernel's memory as /dev/hmem. Signed off by Hariprasad Nellitheertha Signed off by Adam Litke --- linux-2.6.8.1-hari/Documentation/devices.txt | 1 linux-2.6.8.1-hari/drivers/char/mem.c | 72 +++++++++++++++++++++++++++ 2 files changed, 73 insertions(+) diff -puN Documentation/devices.txt~kd-hmem-268 Documentation/devices.txt --- linux-2.6.8.1/Documentation/devices.txt~kd-hmem-268 2004-08-17 17:11:26.000000000 +0530 +++ linux-2.6.8.1-hari/Documentation/devices.txt 2004-08-17 17:11:32.000000000 +0530 @@ -100,6 +100,7 @@ Your cooperation is appreciated. 9 = /dev/urandom Faster, less secure random number gen. 10 = /dev/aio Asyncronous I/O notification interface 11 = /dev/kmsg Writes to this come out as printk's + 12 = /dev/hmem Access to kexec-ed crash dump 1 block RAM disk 0 = /dev/ram0 First RAM disk 1 = /dev/ram1 Second RAM disk diff -puN drivers/char/mem.c~kd-hmem-268 drivers/char/mem.c --- linux-2.6.8.1/drivers/char/mem.c~kd-hmem-268 2004-08-17 17:11:26.000000000 +0530 +++ linux-2.6.8.1-hari/drivers/char/mem.c 2004-08-17 17:11:32.000000000 +0530 @@ -263,6 +263,68 @@ ssize_t copy_hmem_page(unsigned long pfn return 0; } +/* + * After a crash-induced kexec, our physical memory layout + * looks like the following: + * + * max_pfn End of memory\ + * /---------|--------------------------------------------\ + * | Section | Section | Section | Section | + * | K | B | A | C | + * \------------------------------------------------------/ + * + * Section K: System memory. The system is fooled to think it + * can only use memory in this area. + * Section A: Backup of 0 - CRASH_BACKUP_SIZE kB from + * the crashed kernel. + * Section B: Untouched memory from last kernel. + * Section C: Untouched memory from last kernel. + * + * In order to present a properly-ordered dump via this device, + * we must reorder the sections per the following: + * + * /---------|--------------------------------------------\ + * | Section | Section | Empty | Section | + * | A | B | Section | C | + * \------------------------------------------------------/ + * + */ +static ssize_t read_hmem(struct file * file, char * buf, + size_t count, loff_t *ppos) +{ + unsigned long pfn; + unsigned curmem_end, backup_start, backup_end; + size_t read=0, csize; + + backup_start = CRASH_BACKUP_BASE / PAGE_SIZE; + backup_end = backup_start + (CRASH_BACKUP_SIZE / PAGE_SIZE); + curmem_end = max_pfn; + + while(count) { + pfn = *ppos / PAGE_SIZE; + + /* Perform translation (see comment above) */ + if (pfn < curmem_end) + pfn += backup_start; + else if ((pfn >= backup_start) && (pfn < backup_end)) + pfn = -1; /* Placeholder so we know to zero page later */ + + if ((pfn != -1) && (pfn > saved_max_pfn)) + return 0; /* EOF */ + + csize = (count > PAGE_SIZE) ? PAGE_SIZE : count; + + if (copy_hmem_page(pfn, buf, csize, 1)) + return -EFAULT; + + buf += csize; + *ppos += csize; + read += csize; + count -= csize; + } + return read; +} + extern long vread(char *buf, char *addr, unsigned long count); extern long vwrite(char *buf, char *addr, unsigned long count); @@ -626,6 +688,7 @@ static int open_port(struct inode * inod #define read_full read_zero #define open_mem open_port #define open_kmem open_mem +#define open_hmem open_mem static struct file_operations mem_fops = { .llseek = memory_lseek, @@ -671,6 +734,11 @@ static struct file_operations full_fops .write = write_full, }; +static struct file_operations hmem_fops = { + .read = read_hmem, + .open = open_hmem, +}; + static ssize_t kmsg_write(struct file * file, const char __user * buf, size_t count, loff_t *ppos) { @@ -725,6 +793,9 @@ static int memory_open(struct inode * in case 11: filp->f_op = &kmsg_fops; break; + case 12: + filp->f_op = &hmem_fops; + break; default: return -ENXIO; } @@ -754,6 +825,7 @@ static const struct { {8, "random", S_IRUGO | S_IWUSR, &random_fops}, {9, "urandom", S_IRUGO | S_IWUSR, &urandom_fops}, {11,"kmsg", S_IRUGO | S_IWUSR, &kmsg_fops}, + {12,"hmem", S_IRUSR | S_IWUSR | S_IRGRP, &hmem_fops}, }; static struct class_simple *mem_class; _