Re: [PATCH v5 1/5] vmcore: Introduce ELF header in new memory feature

[Michael Holzheu <holzheu@linux.vnet.ibm.com>]

On Fri, 14 Jun 2013 14:54:02 -0400
Vivek Goyal <vgoyal@redhat.com> wrote:

> On Fri, Jun 07, 2013 at 06:55:57PM +0200, Michael Holzheu wrote:
> 
> [..]
> > @@ -935,10 +967,17 @@ static int __init vmcore_init(void)
> >  {
> >  	int rc = 0;
> >  
> > -	/* If elfcorehdr= has been passed in cmdline, then capture the dump.*/
> > -	if (!(is_vmcore_usable()))
> > -		return rc;
> > +	/*
> > +	 * If elfcorehdr= has not been passed in cmdline, try to get the
> > +	 * header from 2nd kernel, then capture the dump.
> > +	 */
> > +	if (!(is_vmcore_usable())) {
> > +		rc = elfcorehdr_alloc();
> > +		if (rc)
> > +			return rc;
> > +	}
> 
> Hi Michael,
> 
> Patch description says that elfcorehdr_alloc() returns the addr and 
> size of elf headers. But that does not seem to be the case here. Has
> it been modified in later patches.

Sorry, that is a relict of one of my previous experiments where I tried
to implement elfcorehdr_addr() similar to the way as you suggest it now.
Because elfcorehdr_addr is a global variable, I decided to not pass
it in the functions. But of course I can change that again if you prefer
that.
 
> Also will it be better if we call elfcorehdr_alloc() always and then
> check for is_vmcore_usable().
> 
> Something like.
> 
> elfcorehdr_addr = elfcorehdr_alloc()
> if (elfcorehdr_addr < )
> 	return elfcorehdr_addr
> 
> if (!(is_vmcore_usable()))
> 	return error

Ok, but then I think elfcorehdr_alloc() should also return
the elfcorehdr_size.

So what about the following patch:
---
 fs/proc/vmcore.c           |   65 +++++++++++++++++++++++++++++++++++++--------
 include/linux/crash_dump.h |    6 ++++
 2 files changed, 60 insertions(+), 11 deletions(-)

--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -123,6 +123,36 @@ static ssize_t read_from_oldmem(char *bu
 	return read;
 }
 
+/*
+ * Architectures may override this function to allocate ELF header in 2nd kernel
+ */
+int __weak elfcorehdr_alloc(unsigned long long *addr, unsigned long long *size)
+{
+	return 0;
+}
+
+/*
+ * Architectures may override this function to free header
+ */
+void __weak elfcorehdr_free(unsigned long long addr)
+{}
+
+/*
+ * Architectures may override this function to read from ELF header
+ */
+ssize_t __weak elfcorehdr_read(char *buf, size_t count, u64 *ppos)
+{
+	return read_from_oldmem(buf, count, ppos, 0);
+}
+
+/*
+ * Architectures may override this function to read from notes sections
+ */
+ssize_t __weak elfcorehdr_read_notes(char *buf, size_t count, u64 *ppos)
+{
+	return read_from_oldmem(buf, count, ppos, 0);
+}
+
 /* Read from the ELF header and then the crash dump. On error, negative value is
  * returned otherwise number of bytes read are returned.
  */
@@ -322,7 +352,7 @@ static int __init update_note_header_siz
 		notes_section = kmalloc(max_sz, GFP_KERNEL);
 		if (!notes_section)
 			return -ENOMEM;
-		rc = read_from_oldmem(notes_section, max_sz, &offset, 0);
+		rc = elfcorehdr_read_notes(notes_section, max_sz, &offset);
 		if (rc < 0) {
 			kfree(notes_section);
 			return rc;
@@ -409,7 +439,8 @@ static int __init copy_notes_elf64(const
 		if (phdr_ptr->p_type != PT_NOTE)
 			continue;
 		offset = phdr_ptr->p_offset;
-		rc = read_from_oldmem(notes_buf, phdr_ptr->p_memsz, &offset, 0);
+		rc = elfcorehdr_read_notes(notes_buf, phdr_ptr->p_memsz,
+					   &offset);
 		if (rc < 0)
 			return rc;
 		notes_buf += phdr_ptr->p_memsz;
@@ -510,7 +541,7 @@ static int __init update_note_header_siz
 		notes_section = kmalloc(max_sz, GFP_KERNEL);
 		if (!notes_section)
 			return -ENOMEM;
-		rc = read_from_oldmem(notes_section, max_sz, &offset, 0);
+		rc = elfcorehdr_read_notes(notes_section, max_sz, &offset);
 		if (rc < 0) {
 			kfree(notes_section);
 			return rc;
@@ -597,7 +628,8 @@ static int __init copy_notes_elf32(const
 		if (phdr_ptr->p_type != PT_NOTE)
 			continue;
 		offset = phdr_ptr->p_offset;
-		rc = read_from_oldmem(notes_buf, phdr_ptr->p_memsz, &offset, 0);
+		rc = elfcorehdr_read_notes(notes_buf, phdr_ptr->p_memsz,
+					   &offset);
 		if (rc < 0)
 			return rc;
 		notes_buf += phdr_ptr->p_memsz;
@@ -793,7 +825,7 @@ static int __init parse_crash_elf64_head
 	addr = elfcorehdr_addr;
 
 	/* Read Elf header */
-	rc = read_from_oldmem((char*)&ehdr, sizeof(Elf64_Ehdr), &addr, 0);
+	rc = elfcorehdr_read((char *)&ehdr, sizeof(Elf64_Ehdr), &addr);
 	if (rc < 0)
 		return rc;
 
@@ -820,7 +852,7 @@ static int __init parse_crash_elf64_head
 	if (!elfcorebuf)
 		return -ENOMEM;
 	addr = elfcorehdr_addr;
-	rc = read_from_oldmem(elfcorebuf, elfcorebuf_sz_orig, &addr, 0);
+	rc = elfcorehdr_read(elfcorebuf, elfcorebuf_sz_orig, &addr);
 	if (rc < 0)
 		goto fail;
 
@@ -849,7 +881,7 @@ static int __init parse_crash_elf32_head
 	addr = elfcorehdr_addr;
 
 	/* Read Elf header */
-	rc = read_from_oldmem((char*)&ehdr, sizeof(Elf32_Ehdr), &addr, 0);
+	rc = elfcorehdr_read((char *)&ehdr, sizeof(Elf32_Ehdr), &addr);
 	if (rc < 0)
 		return rc;
 
@@ -875,7 +907,7 @@ static int __init parse_crash_elf32_head
 	if (!elfcorebuf)
 		return -ENOMEM;
 	addr = elfcorehdr_addr;
-	rc = read_from_oldmem(elfcorebuf, elfcorebuf_sz_orig, &addr, 0);
+	rc = elfcorehdr_read(elfcorebuf, elfcorebuf_sz_orig, &addr);
 	if (rc < 0)
 		goto fail;
 
@@ -902,7 +934,7 @@ static int __init parse_crash_elf_header
 	int rc=0;
 
 	addr = elfcorehdr_addr;
-	rc = read_from_oldmem(e_ident, EI_NIDENT, &addr, 0);
+	rc = elfcorehdr_read(e_ident, EI_NIDENT, &addr);
 	if (rc < 0)
 		return rc;
 	if (memcmp(e_ident, ELFMAG, SELFMAG) != 0) {
@@ -935,7 +967,14 @@ static int __init vmcore_init(void)
 {
 	int rc = 0;
 
-	/* If elfcorehdr= has been passed in cmdline, then capture the dump.*/
+	/* Allow architectures to allocate ELF header in 2nd kernel */
+	rc = elfcorehdr_alloc(&elfcorehdr_addr, &elfcorehdr_size);
+	if (rc)
+		return rc;
+	/*
+	 * If elfcorehdr= has been passed in cmdline or created in 2nd kernel,
+	 * then capture the dump.
+	 */
 	if (!(is_vmcore_usable()))
 		return rc;
 	rc = parse_crash_elf_headers();
@@ -943,7 +982,11 @@ static int __init vmcore_init(void)
 		pr_warn("Kdump: vmcore not initialized\n");
 		return rc;
 	}
-
+	elfcorehdr_free(elfcorehdr_addr);
+	/*
+	 * elfcorehdr_addr must not be set to NULL here to keep
+	 * is_kdump_kernel() working.
+	 */
 	proc_vmcore = proc_create("vmcore", S_IRUSR, NULL, &proc_vmcore_operations);
 	if (proc_vmcore)
 		proc_vmcore->size = vmcore_size;
--- a/include/linux/crash_dump.h
+++ b/include/linux/crash_dump.h
@@ -12,6 +12,12 @@
 extern unsigned long long elfcorehdr_addr;
 extern unsigned long long elfcorehdr_size;
 
+extern int __weak elfcorehdr_alloc(unsigned long long *addr,
+				   unsigned long long *size);
+extern void __weak elfcorehdr_free(unsigned long long addr);
+extern ssize_t __weak elfcorehdr_read(char *buf, size_t count, u64 *ppos);
+extern ssize_t __weak elfcorehdr_read_notes(char *buf, size_t count, u64 *ppos);
+
 extern ssize_t copy_oldmem_page(unsigned long, char *, size_t,
 						unsigned long, int);