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Violators will be prosecuted for from ; Mon, 12 Feb 2018 07:25:25 -0700 From: Daniel Henrique Barboza Date: Mon, 12 Feb 2018 12:25:06 -0200 In-Reply-To: <20180212142506.28445-1-danielhb@linux.vnet.ibm.com> References: <20180212142506.28445-1-danielhb@linux.vnet.ibm.com> Message-Id: <20180212142506.28445-2-danielhb@linux.vnet.ibm.com> Subject: [Qemu-devel] [PATCH v3 1/1] dump.c: allow fd_write_vmcore to return errno on failure List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: marcandre.lureau@redhat.com, eblake@redhat.com, Yasmin Beatriz , Jose Ricardo Ziviani , Daniel Henrique Barboza From: Yasmin Beatriz 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 --- dump.c | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-) diff --git a/dump.c b/dump.c index 7b13baa413..171ff8a3b8 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; } -- 2.14.3