[PATCH v1 6/7] crashdump: create get_elfcorehdrsz()

[Eric DeVolder]

This routine provides a means to tune the size of the elfcorehdr
buffer segment, taking into account the --hotplug and
--elfcorehdrsz options. The possibilities are:

                 no --elfcorehdrsz  w/ --elfcorehdrsz
  no --hotplug   just-large-enough  user-specified
  w/ --hotplug   maximum-size       user-specified

Where just-large-enough is the min_size parameter, computed based
upon the existing CPUs and memory regions in the system.

Where maximum-size is computed based upon the maximum number of
CPUs and memory regions possible in the system.

Signed-off-by: Eric DeVolder <eric.devolder at oracle.com>
---
 include/elf.h     |  2 ++
 kexec/crashdump.c | 33 +++++++++++++++++++++++++++++++++
 kexec/crashdump.h |  4 ++++
 3 files changed, 39 insertions(+)

diff --git a/include/elf.h b/include/elf.h
index 1c8d2cc..2c5884d 100644
--- a/include/elf.h
+++ b/include/elf.h
@@ -163,6 +163,8 @@ typedef struct
 
 #define EI_PAD		9		/* Byte index of padding bytes */
 
+#define PN_XNUM 0xffff		/* Maximum number of headers in e_phnum */
+
 /* Legal values for e_type (object file type).  */
 
 #define ET_NONE		0		/* No file type */
diff --git a/kexec/crashdump.c b/kexec/crashdump.c
index 0b363c5..4210c53 100644
--- a/kexec/crashdump.c
+++ b/kexec/crashdump.c
@@ -53,6 +53,9 @@
 #undef EHDR
 #undef FUNC
 
+#define MIN(x, y) ((x) < (y) ? (x) : (y))
+#define MAX(x, y) ((x) > (y) ? (x) : (y))
+
 unsigned long crash_architecture(struct crash_elf_info *elf_info)
 {
 	if (xen_present())
@@ -157,3 +160,33 @@ int get_kernel_vmcoreinfo(uint64_t *addr, uint64_t *len)
 {
 	return get_vmcoreinfo("/sys/kernel/vmcoreinfo", addr, len);
 }
+
+unsigned long get_elfcorehdrsz(struct crash_elf_info *elf_info,
+			       unsigned long min_size,
+			       unsigned long nr_memory_ranges)
+{
+	/* Size elfcorehdr appropriately */
+	unsigned long sz = min_size;
+
+	if (elfcorehdrsz) {
+		/* Utilize option value */
+		sz = elfcorehdrsz;
+	} else {
+		/* Compute maximum for hotplug */
+		if (do_hotplug) {
+			long int nr_cpus = get_nr_cpus();
+			sz = nr_cpus + nr_memory_ranges;
+			sz = MIN(sz, PN_XNUM);
+				if (elf_info->class == ELFCLASS32) {
+					sz *= sizeof(Elf32_Phdr);
+					sz += sizeof(Elf32_Ehdr);
+				} else {
+					sz *= sizeof(Elf64_Phdr);
+					sz += sizeof(Elf64_Ehdr);
+				}
+		}
+		/* else default is min_size */
+	}
+	sz = MAX(min_size, sz);
+	return sz;
+}
diff --git a/kexec/crashdump.h b/kexec/crashdump.h
index 28d3278..e4cedce 100644
--- a/kexec/crashdump.h
+++ b/kexec/crashdump.h
@@ -53,6 +53,10 @@ int crash_create_elf64_headers(struct kexec_info *info,
 
 unsigned long crash_architecture(struct crash_elf_info *elf_info);
 
+unsigned long get_elfcorehdrsz(struct crash_elf_info *elf_info,
+			       unsigned long min_size,
+			       unsigned long nr_memory_ranges);
+
 unsigned long phys_to_virt(struct crash_elf_info *elf_info,
 			   unsigned long long paddr);
 
-- 
2.31.1