From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37342) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1elGMQ-0004Z1-B0 for qemu-devel@nongnu.org; Mon, 12 Feb 2018 10:49:43 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1elGMN-0001Rf-He for qemu-devel@nongnu.org; Mon, 12 Feb 2018 10:49:42 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:42782) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1elGMN-0001Ph-8V for qemu-devel@nongnu.org; Mon, 12 Feb 2018 10:49:39 -0500 Received: from pps.filterd (m0098396.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w1CFnPIF128582 for ; Mon, 12 Feb 2018 10:49:37 -0500 Received: from e12.ny.us.ibm.com (e12.ny.us.ibm.com [129.33.205.202]) by mx0a-001b2d01.pphosted.com with ESMTP id 2g3d49aber-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 12 Feb 2018 10:49:36 -0500 Received: from localhost by e12.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 12 Feb 2018 10:49:35 -0500 References: <20180212142506.28445-1-danielhb@linux.vnet.ibm.com> <20180212142506.28445-2-danielhb@linux.vnet.ibm.com> <98934c2f-2210-83d7-d629-157e5a7cee8e@linux.vnet.ibm.com> From: Daniel Henrique Barboza Date: Mon, 12 Feb 2018 13:49:30 -0200 MIME-Version: 1.0 In-Reply-To: <98934c2f-2210-83d7-d629-157e5a7cee8e@linux.vnet.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Message-Id: <9bdd6f79-05e2-48ab-385a-70b6a3ac207c@linux.vnet.ibm.com> Subject: Re: [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: Murilo Opsfelder Araujo , qemu-devel@nongnu.org Cc: marcandre.lureau@redhat.com, Yasmin Beatriz , Jose Ricardo Ziviani On 02/12/2018 12:46 PM, Murilo Opsfelder Araujo wrote: > On 02/12/2018 12:25 PM, Daniel Henrique Barboza wrote: >> 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"); > Do we need -ret passed to error_setg_errno()? fd_write_vmcore() returns > negative errno in case of error. I am passing -ret here to provide a positive errno value to error_setg_errno. I am not sure if os_error can be negative and didn't want to risk strerror() breaking. Daniel > > Cheers > Murilo