Re: [PATCH] Core dump file control

Michael Sinz
2002-02-14T17:53:52Z

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Michael Sinz wrote:
>
> I have, for a long time, wished that Linux had a way to specify where
> core dumps are stored and what the name of the core dump is. Now that
> I have been building large linux clusters with many diskless nodes,
> this need has become even more important.

[...]

This patch is the one for Linux 2.5.4 (albeit not as heavily tested)

--
Michael Sinz ---- Worldgate Communications ---- msinz@wgate.com
A master's secrets are only as good as
the master's ability to explain them to others.

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diff -urP linux-2.5.4/fs/exec.c linux-2.5.4-patch/fs/exec.c
--- linux-2.5.4/fs/exec.c Sun Feb 10 20:50:15 2002
+++ linux-2.5.4-patch/fs/exec.c Thu Feb 14 12:45:00 2002
@@ -35,6 +35,7 @@
#include <linux/highmem.h>
#include <linux/spinlock.h>
#include <linux/personality.h>
+#include <linux/utsname.h>
#include <linux/binfmts.h>
#define __NO_VERSION__
#include <linux/module.h>
@@ -49,6 +50,12 @@

int core_uses_pid;

+/* The format string for the core file name...
+ We default to "core" such that past behavior
+ remains unchanged. The 64 character limit is
+ arbitrary but must match the sysctl table. */
+char core_name_format[64] = {"core"};
+
static struct linux_binfmt *formats;
static rwlock_t binfmt_lock = RW_LOCK_UNLOCKED;

@@ -934,14 +941,37 @@
__MOD_DEC_USE_COUNT(old->module);
}

+/* This is the maximum expanded core file name. We use
+ a reasonable number here since we use the stack to
+ do the expansion. However, the number should be big
+ enough to handle a reasonable command name plus PID
+ and/or UID in addition to the file name part that
+ is in the core_name_format string. */
+#define MAX_CORE_NAME (160)
+
int do_coredump(long signr, struct pt_regs * regs)
{
struct linux_binfmt * binfmt;
- char corename[6+sizeof(current->comm)+10];
struct file * file;
struct inode * inode;
int retval = 0;

+ int fmt_i;
+ int name_n;
+ int addPID;
+ char *cname;
+
+ /* The +11 is here to simplify the code path. What
+ we do is always check that we are less than MAX
+ but there are times when we also need to append
+ a number (such as the PID or UID). Rather than
+ using another temporary buffer, we provide for
+ enough extra space such that those numbers can
+ be added in one gulp even if we are just under
+ the MAX_CORE_NAME. Reduction in complexity of
+ the code path means a more reliable implementation. */
+ char corename[MAX_CORE_NAME + 1 + 11];
+
lock_kernel();
binfmt = current->binfmt;
if (!binfmt || !binfmt->core_dump)
@@ -952,10 +982,92 @@
if (current->rlim[RLIMIT_CORE].rlim_cur < binfmt->min_coredump)
goto fail;

- memcpy(corename,"core.", 5);
- corename[4] = '\0';
- if (core_uses_pid || atomic_read(&current->mm->mm_users) != 1)
- sprintf(&corename[4], ".%d", current->pid);
+ /* Set this to true if we are going to add the PID. If the PID
+ already is added in the format we will end up clearing this.
+ The purpose is to provide for the old behavior of adding the
+ PID to the core file name but to not add it if it already
+ was included via the file name format pattern. */
+ addPID = (core_uses_pid || atomic_read(&current->mm->mm_users) != 1);
+
+ /* Build the core file name as needed from the format string */
+ for (fmt_i=0, name_n=0;
+ name_n < MAX_CORE_NAME && core_name_format[fmt_i];
+ fmt_i++)
+ {
+ switch (core_name_format[fmt_i])
+ {
+ case '%': /* A format character */
+ fmt_i++;
+ switch (core_name_format[fmt_i])
+ {
+ case '%': /* The way we get this character */
+ corename[name_n++] = '%';
+ break;
+
+ case 'N': /* Process name */
+ cname=current->comm;
+
+ /* Only copy as much as will fit within the
+ MAX_CORE_NAME */
+ while (*cname && (name_n < MAX_CORE_NAME))
+ {
+ if (*cname != '/')
+ corename[name_n++] = *cname;
+ cname++;
+ }
+ break;
+
+ case 'H': /* Node name */
+ cname=system_utsname.nodename;
+
+ /* Only copy as much as will fit within the
+ MAX_CORE_NAME */
+ while (*cname && (name_n < MAX_CORE_NAME))
+ {
+ if (*cname != '/')
+ corename[name_n++] = *cname;
+ cname++;
+ }
+ break;
+
+ case 'P': /* Process PID */
+ /* Since we are adding it here, don't append */
+ addPID=0;
+
+ /* We don't need to pre-check that the number
+ fits since we added a padding of 11
+ characters to the end of the string buffer
+ just so that we don't need to do an extra
+ check */
+ name_n += sprintf(&corename[name_n],"%d",current->pid);
+ break;
+
+ case 'U': /* UID of the process */
+ /* We don't need to pre-check that the number
+ fits since we added a padding of 11
+ characters to the end of the string buffer
+ just so that we don't need to do an extra
+ check */
+ name_n += sprintf(&corename[name_n],"%d",current->uid);
+ break;
+ }
+ break;
+
+ default: /* Anything else just pass along */
+ corename[name_n++] = core_name_format[fmt_i];
+ }
+ }
+
+ /* If we still want to append the PID and there is room, do so */
+ /* This is to preserve current behavior */
+ if (addPID && (name_n < MAX_CORE_NAME))
+ {
+ name_n += sprintf(&corename[name_n],".%d",current->pid);
+ }
+
+ /* And make sure to null terminate the string */
+ corename[name_n]='\0';
+
file = filp_open(corename, O_CREAT | 2 | O_NOFOLLOW, 0600);
if (IS_ERR(file))
goto fail;
diff -urP linux-2.5.4/include/linux/sysctl.h linux-2.5.4-patch/include/linux/sysctl.h
--- linux-2.5.4/include/linux/sysctl.h Sun Feb 10 20:50:07 2002
+++ linux-2.5.4-patch/include/linux/sysctl.h Thu Feb 14 12:43:52 2002
@@ -124,6 +124,7 @@
KERN_CORE_USES_PID=52, /* int: use core or core.%pid */
KERN_TAINTED=53, /* int: various kernel tainted flags */
KERN_CADPID=54, /* int: PID of the process to notify on CAD */
+ KERN_CORE_NAME_FORMAT=55, /* string: core file name format string */
};

diff -urP linux-2.5.4/kernel/sysctl.c linux-2.5.4-patch/kernel/sysctl.c
--- linux-2.5.4/kernel/sysctl.c Sun Feb 10 20:50:09 2002
+++ linux-2.5.4-patch/kernel/sysctl.c Thu Feb 14 12:43:52 2002
@@ -50,6 +50,7 @@
extern int max_queued_signals;
extern int sysrq_enabled;
extern int core_uses_pid;
+extern char core_name_format[];
extern int cad_pid;

/* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
@@ -172,6 +173,8 @@
0644, NULL, &proc_dointvec},
{KERN_CORE_USES_PID, "core_uses_pid", &core_uses_pid, sizeof(int),
0644, NULL, &proc_dointvec},
+ {KERN_CORE_NAME_FORMAT, "core_name_format", core_name_format, 64,
+ 0644, NULL, &proc_doutsstring, &sysctl_string},
{KERN_TAINTED, "tainted", &tainted, sizeof(int),
0644, NULL, &proc_dointvec},
{KERN_CAP_BSET, "cap-bound", &cap_bset, sizeof(kernel_cap_t),