From 0c33659d09f4a8ab926846295538d6a67e8c2c63 Mon Sep 17 00:00:00 2001 From: Yasmin Beatriz Date: Mon, 12 Feb 2018 12:25:06 -0200 Subject: [PATCH 1/2] dump.c: allow fd_write_vmcore to return errno on failure MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit fd_write_vmcore can fail to execute for a lot of reasons that can be retrieved by errno, but it only returns -1. This makes difficult for the caller to know what happened and only a generic error message is propagated back to the user. This is an example using dump-guest-memory: (qemu) dump-guest-memory /home/yasmin/mnt/test.dump dump: failed to save memory All callers of fd_write_vmcore of dump.c does error handling via error_setg(), so at first it seems feasible to add the Error pointer as an argument of fd_write_vmcore. This proved to be more complex than it first looked. fd_write_vmcore is used by write_elf64_notes and write_elf32_notes as a WriteCoreDumpFunction prototype. WriteCoreDumpFunction is declared in include/qom/cpu.h and is used all around the code. This leaves us with few alternatives: - change the WriteCoreDumpFunction prototype to include an error pointer. This would require to change all functions that implements this prototype to also receive an Error pointer; - change both write_elf64_notes and write_elf32_notes to no use the WriteCoreDumpFunction. These functions use not only fd_write_vmcore but also buf_write_note, so this would require to change buf_write_note to handle an Error pointer. Considerable easier than the alternative above, but it's still a lot of code just for the benefit of the callers of fd_write_vmcore. This patch presents an easier solution that benefits all fd_write_vmcore callers: - instead of returning -1 on error, return -errno. All existing callers already checks for ret < 0 so there is no need to change the caller's logic too much. This also allows the retrieval of the errno. - all callers were updated to use error_setg_errno instead of just errno_setg. Now that fd_write_vmcore can return an errno, let's update all callers so they can benefit from a more detailed error message. This is the same dump-guest-memory example with this patch applied: (qemu) dump-guest-memory /home/yasmin/mnt/test.dump dump: failed to save memory: No space left on device (qemu) This example illustrates an error of fd_write_vmcore when called from write_data. All other callers will benefit from better error messages as well. Reported-by: yilzhang@redhat.com Cc: Jose Ricardo Ziviani Signed-off-by: Yasmin Beatriz Signed-off-by: Daniel Henrique Barboza Message-Id: <20180212142506.28445-2-danielhb@linux.vnet.ibm.com> Reviewed-by: Eric Blake Reviewed-by: Marc-André Lureau Signed-off-by: Marc-André Lureau --- dump.c | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-) diff --git a/dump.c b/dump.c index 6bdb0dbe23..669f715274 100644 --- a/dump.c +++ b/dump.c @@ -107,7 +107,7 @@ static int fd_write_vmcore(const void *buf, size_t size, void *opaque) written_size = qemu_write_full(s->fd, buf, size); if (written_size != size) { - return -1; + return -errno; } return 0; @@ -140,7 +140,7 @@ static void write_elf64_header(DumpState *s, Error **errp) ret = fd_write_vmcore(&elf_header, sizeof(elf_header), s); if (ret < 0) { - error_setg(errp, "dump: failed to write elf header"); + error_setg_errno(errp, -ret, "dump: failed to write elf header"); } } @@ -171,7 +171,7 @@ static void write_elf32_header(DumpState *s, Error **errp) ret = fd_write_vmcore(&elf_header, sizeof(elf_header), s); if (ret < 0) { - error_setg(errp, "dump: failed to write elf header"); + error_setg_errno(errp, -ret, "dump: failed to write elf header"); } } @@ -194,7 +194,8 @@ static void write_elf64_load(DumpState *s, MemoryMapping *memory_mapping, ret = fd_write_vmcore(&phdr, sizeof(Elf64_Phdr), s); if (ret < 0) { - error_setg(errp, "dump: failed to write program header table"); + error_setg_errno(errp, -ret, + "dump: failed to write program header table"); } } @@ -217,7 +218,8 @@ static void write_elf32_load(DumpState *s, MemoryMapping *memory_mapping, ret = fd_write_vmcore(&phdr, sizeof(Elf32_Phdr), s); if (ret < 0) { - error_setg(errp, "dump: failed to write program header table"); + error_setg_errno(errp, -ret, + "dump: failed to write program header table"); } } @@ -237,7 +239,8 @@ static void write_elf64_note(DumpState *s, Error **errp) ret = fd_write_vmcore(&phdr, sizeof(Elf64_Phdr), s); if (ret < 0) { - error_setg(errp, "dump: failed to write program header table"); + error_setg_errno(errp, -ret, + "dump: failed to write program header table"); } } @@ -302,7 +305,8 @@ static void write_elf32_note(DumpState *s, Error **errp) ret = fd_write_vmcore(&phdr, sizeof(Elf32_Phdr), s); if (ret < 0) { - error_setg(errp, "dump: failed to write program header table"); + error_setg_errno(errp, -ret, + "dump: failed to write program header table"); } } @@ -355,7 +359,8 @@ static void write_elf_section(DumpState *s, int type, Error **errp) ret = fd_write_vmcore(&shdr, shdr_size, s); if (ret < 0) { - error_setg(errp, "dump: failed to write section header table"); + error_setg_errno(errp, -ret, + "dump: failed to write section header table"); } } @@ -365,7 +370,7 @@ static void write_data(DumpState *s, void *buf, int length, Error **errp) ret = fd_write_vmcore(buf, length, s); if (ret < 0) { - error_setg(errp, "dump: failed to save memory"); + error_setg_errno(errp, -ret, "dump: failed to save memory"); } else { s->written_size += length; } From 4b17bc933fc26f7a4a306a43597f4d97e3c2dc38 Mon Sep 17 00:00:00 2001 From: Andrew Jones Date: Wed, 14 Mar 2018 16:38:20 +0100 Subject: [PATCH 2/2] dump-guest-memory: more descriptive lookup_type failure MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit We've seen a few reports of (gdb) source /usr/share/qemu-kvm/dump-guest-memory.py Traceback (most recent call last): File "/usr/share/qemu-kvm/dump-guest-memory.py", line 19, in UINTPTR_T = gdb.lookup_type("uintptr_t") gdb.error: No type named uintptr_t. This occurs when symbols haven't been loaded first, i.e. neither a QEMU binary was loaded nor a QEMU process was attached first. Let's better inform the user of how to fix the issue themselves in order to avoid more reports. Acked-by: Janosch Frank Signed-off-by: Andrew Jones Message-Id: <20180314153820.18426-1-drjones@redhat.com> Reviewed-by: Fam Zheng Tested-by: Fam Zheng Reviewed-by: Laszlo Ersek Reviewed-by: Marc-André Lureau Signed-off-by: Marc-André Lureau --- scripts/dump-guest-memory.py | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/scripts/dump-guest-memory.py b/scripts/dump-guest-memory.py index 51acfcd0c0..276eebf0c2 100644 --- a/scripts/dump-guest-memory.py +++ b/scripts/dump-guest-memory.py @@ -16,7 +16,12 @@ the COPYING file in the top-level directory. import ctypes import struct -UINTPTR_T = gdb.lookup_type("uintptr_t") +try: + UINTPTR_T = gdb.lookup_type("uintptr_t") +except Exception as inst: + raise gdb.GdbError("Symbols must be loaded prior to sourcing dump-guest-memory.\n" + "Symbols may be loaded by 'attach'ing a QEMU process id or by " + "'load'ing a QEMU binary.") TARGET_PAGE_SIZE = 0x1000 TARGET_PAGE_MASK = 0xFFFFFFFFFFFFF000